topheader Welcome 35.172.217.40 @ xps.scios.ch on Mon Dec 9 14:49:36 CET 2019
 
topheader
 

Table of Contents

CLIPS BPG


Reference Manual


Volume I

Basic Programming Guide


XSI/CLIPS Basic Programming Guide

Version 6.xx January 2010


The History of CLIPS


The origins of the C Language Integrated Production System (CLIPS) date back to 1984 at NASA’s Johnson Space Center. At this time, the Artificial Intelligence Section had developed over a dozen prototype expert systems applications using state of the art hardware and software. However, despite extensive demonstrations of the potential of expert systems, few of these applications were put into regular use. This failure to provide expert systems technology within NASA’s operational computing constraints could largely be traced to the use of LISP as the base language for nearly all expert system software tools at that time. In particular, three problems hindered the use of LISP based expert system tools within NASA: the low availability of LISP on a wide variety of conventional computers, the high cost of state of the art LISP tools and hardware, and the poor integra­tion of LISP with other languages (making embedded applications difficult).


The Artificial Intelligence Section felt that the use of a conventional language, such as C, would eliminate most of these problems, and initially looked to the expert system tool vendors to provide an expert system tool written using a conventional language. Although a number of tool vendors started converting their tools to run in C, the cost of each tool was still very high, most were restricted to a small variety of computers, and the projected availability times were discouraging. To meet all of its needs in a timely and cost effective manner, it became evident that the Artificial Intelligence Section would have to develop its own C based expert system tool.


The prototype version of CLIPS was developed in the spring of 1985 in a little over two months. Particular attention was given to making the tool compatible with expert systems under development at that time by the Artificial Intelligence Section. Thus, the syntax of CLIPS was made to very closely resemble the syntax of a subset of the ART expert system tool developed by Inference Corporation. Although originally modelled from ART, CLIPS was developed entirely without assistance from Inference or access to the ART source code.


The original intent for CLIPS was to gain useful insight and knowledge about the construction of expert system tools and to lay the groundwork for the construction of a replacement tool for the commercial tools currently being used. Version 1.0 demonstrated the feasibility of the project concept. After additional development, it became apparent that CLIPS would be a low cost expert system tool ideal for the purposes of training. Another year of development and internal use went into CLIPS improving its portability, performance, functionality, and supporting documentation. Version 3.0 of CLIPS was made available to groups outside of NASA in the summer of 1986.2


Further enhancements transformed CLIPS from a training tool into a tool useful for the development and delivery of expert systems as well. Versions 4.0 and 4.1 of CLIPS, released respectively in the summer and fall of 1987, featured greatly improved performance, external language integration, and delivery capabilities. Version 4.2 of CLIPS, released in the summer of 1988, was a complete rewrite of CLIPS for code modularity. Also included with this release were an architecture manual providing a detailed description of the CLIPS software architecture and a utility program for aiding in the verification and validation of rule based programs. Version 4.3 of CLIPS, released in the summer of 1989, added still more functionality.


Originally, the primary representation methodology in CLIPS was a forward chaining rule lan­guage based on the Rete algorithm (hence the Production System part of the CLIPS acronym). Version 5.0 of CLIPS, released in the spring of 1991, introduced two new programming paradigms: procedural programming (as found in languages such as C and Ada) and object oriented programming (as found in languages such as the Common Lisp Object System and Smalltalk). The object oriented programming language provided within CLIPS is called the CLIPS Object Oriented Language (COOL). Version 5.1 of CLIPS, released in the fall of 1991, was primarily a software maintenance upgrade required to support the newly developed and/or enhanced X Window, MS DOS, and Macintosh interfaces. Version 6.0 of CLIPS, released in 1993, provided support for the development of modular programs and tight integration between the object-oriented and rule-based programming capabilities of CLIPS. Version 6.1 of CLIPS, released in 1998, removed support for older non-ANSI C Compilers and added support for C++ compilers. Commands to profile the time spent in constructs and user-defined functions were also added.


CLIPS is now maintained independently from NASA as public domain software.


Because of its portability, extensibility, capabilities, and low cost, CLIPS has received widespread acceptance throughout the government, industry, and academia. The development of CLIPS has helped to improve the ability to deliver expert system technology throughout the public and private sectors for a wide range of applications and diverse computing environments. See appendix A of the Basic Programming Guide for information on obtaining CLIPS and support.


CLIPS Version 6.2+


Version 6.2 of CLIPS contains two major enhancements. First, CLIPS now provides a mechanism which allows an embedded application to create multiple environments into which programs can be loaded. Second, an improved Windows 95/98/NT CLIPS interface is now available and the Macintosh CLIPS interface has been enhanced to support MacOS X. For a detailed listing of differences between the 6.x releases of CLIPS, refer to appendix B of the Basic Programming Guide and appendix C of the Advanced Programming Guide.

CLIPS Documentation

Two documents are provided with CLIPS.

The CLIPS Reference Manual which is split into the following parts:

  • Volume I - The Basic Programming Guide, which provides the definitive description of CLIPS syntax and examples of usage.
  • Volume II - The Advanced Programming Guide, which provides detailed discus­sions of the more sophisticated features in CLIPS and is intended for people with extensive programming experience who are using CLIPS for advanced ap­plications.
  • Volume III - The Interfaces Guide, which provides information on machine specific interfaces.
  • The CLIPS User’s Guide which provides an introduction to CLIPS rule based and object oriented programming and is intended for people with little or no expert system experience.


Acknowledgements

As with any large project, CLIPS is the result of the efforts of numerous people. The primary contributors have been: Robert Savely, who conceived the project and provided overall direction and support; Chris Culbert, who managed the project and wrote the original CLIPS Reference Manual; Gary Riley, who designed and developed the rule based portion of CLIPS, co authored the CLIPS Reference Manual, and developed the Macintosh interface for CLIPS; Brian Donnell, who designed and developed the CLIPS Object Oriented Language (COOL) and co authored the CLIPS Reference Manual; Bebe Ly, who developed the X Window interface for CLIPS; Chris Ortiz, who developed the original Windows 95 interface for CLIPS; Dr. Joseph Giarratano of the University of Houston-Clear Lake, who wrote the CLIPS User’s Guide; and Frank Lopez, who designed and developed CLIPS version 1.0 and wrote the CLIPS 1.0 User’s Guide.


Many other individuals contributed to the design, development, review, and general support of CLIPS, including: Jack Aldridge, Carla Armstrong, Paul Baffes, Ann Baker, Stephen Baudendistel, Les Berke, Tom Blinn, Marlon Boarnet, Dan Bochsler, Bob Brown, Barry Cameron, Tim Cleghorn, Major Paul Condit, Major Steve Cross, Andy Cunningham, Dan Danley, Mark Engelberg, Kirt Fields, Ken Freeman, Kevin Greiner, Ervin Grice, Sharon Hecht, Patti Herrick, Mark Hoffman, Grace Hua, Gordon Johnson, Phillip Johnston, Sam Juliano, Ed Lineberry, Bowen Loftin, Linda Martin, Daniel McCoy, Terry McGregor, Becky McGuire, Scott Meadows, C. J. Melebeck, Paul Mitchell, Steve Mueller, Bill Paseman, Cynthia Rathjen, Eric Raymond, Reza Razavipour, Marsha Renals, Monica Rua, Tim Saito, Michael Sullivan, Gregg Swietek, Eric Taylor, James Villarreal, Lui Wang, Bob Way, Jim Wescott, Charlie Wheeler, and Wes White.

Section 1   Introduction

This manual is the Basic Programming Guide for CLIPS. It is intended for users interested in the syntax of CLIPS. No previous expert system background is required, al­though a general understanding of computer languages is assumed. Section 2 of this manual provides an overview of the CLIPS language and basic terminology. Sections 3 through 11 provide additional details regarding the CLIPS programming language on topics such as rules and the CLIPS Object Oriented Programming Language (COOL). The types of actions and functions provided by CLIPS are defined in section 12. Finally, commands typically used from the CLIPS interactive interface are described in section 13.


The Basic Programming Guide documents just the basic CLIPS syntax. More advanced capabilities, such as user defined functions, embedded applications, etc., are docu­mented more fully in the Advanced Programming Guide. The Advanced Programming Guide is intended for users who have a complete knowledge of the CLIPS syntax and a programming background. It is not necessary to read the Advanced Program­ming Guide to learn how to use CLIPS. CLIPS can be learned and simple expert systems can be built with the information provided in this manual.

Section 2   CLIPS Overview

This section gives a general overview of CLIPS and of the basic concepts used through­out this manual.

2.1 Interacting with CLIPS

CLIPS expert systems may be executed in three ways: interactively using a simple, text oriented, command prompt interface; interactively using a window/menu/mouse interface on certain ma­chines; or as embedded expert systems in which the user provides a main pro­gram and controls execution of the expert system. Embedded applications are dis­cussed in the Advanced Programming Guide. In addition, a series of commands can be automatically read di­rectly from a file when CLIPS is first started or as the result of the batch command.


The generic CLIPS interface is a simple, interactive, text oriented, command prompt interface for high porta­bility. The stan­dard usage is to create or edit a knowledge base using any standard text editor, save the knowledge base as one or more text files, exit the editor and execute CLIPS, then load the knowledge base into CLIPS. The in­terface provides commands for viewing the current state of the sys­tem, tracing execu­tion, adding or removing information, and clearing CLIPS.


A more sophisticated window interface is available for the Macintosh, Windows 3.1, and X Window environments. All interface commands described in this section are available in the window interfaces. These interfaces are described in more detail in the Interfaces Guide.

2.1.1 Top Level Commands

The primary method for interacting with CLIPS in a non embedded environment is through the CLIPS command prompt (or top level). When the “CLIPS>” prompt is printed, a command may be entered for evaluation. Commands may be function calls, constructs, global variables, or constants. If a function call is entered (see section 2.3.2), that function is evaluated and its return value is printed. Function calls in CLIPS use a prefix notation—the operands to a function always appear after the function name. Entering a construct definition (see section 2.3.3) at the CLIPS prompt creates a new construct of the appropriate type. Entering a global variable (see section 2.4.3) causes the value of the global variable to be printed. Entering a constant (see section 2.3.1) at the top level causes the constant to be printed (which is not very useful). For example,


CLIPS (V6.0 05/12/93)

CLIPS> (+ 3 4)

7

CLIPS> (defglobal ?*x* = 3)

CLIPS> ?*x*

3

CLIPS> red

red

CLIPS>


The previous example first called the addition function adding the numbers 3 and 4 to yield the result 7. A global variable ?*x* was then defined and given the value 3. The variable ?*x* was then entered at the prompt and its value of 3 was returned. Finally the constant symbol red was entered and was returned (since a constant evaluates to itself).

2.1.2 Automated Command Entry and Loading

Some operating systems allow additional arguments to be specified to a program when it begins execution. When the CLIPS executable is started under such an operating system, CLIPS can be made to automatically execute a series of commands read directly from a file or to load constructs from a file. The command line syntax for starting CLIPS and automatically reading commands or loading constructs from a file is as follows:

Syntax

clips <option>*


<option> ::= -f <filename> |

-f2 <filename> |

-l <filename>


For the  f option, <filename> is a file that contains CLIPS commands. If the exit command is included in the file, CLIPS will halt and the user is returned to the operat­ing system after executing the commands in the file. If an exit command is not in the file, CLIPS will enter in its interactive state after executing the commands in the file. Commands in the file should be entered exactly as they would be interactively (i.e. opening and closing parentheses must be included and a carriage return must be at the end of the command). The  f command line option is equivalent to interactively entering a batch command as the first command to the CLIPS prompt.


The -f2 option is similar to the -f option, but is equivalent to interactively entering a batch* command. The commands stored in <filename> are immediately executed, but the commands and their return values are not displayed as they would be for a batch command.


For the -l option, <filename> should be a file containing CLIPS constructs. This file will be loaded into the environment. The  l command line option is equivalent to interactively entering a load command.

2.1.3 Integration with Other Languages

When using an expert system, two kinds of integration are important: embedding CLIPS in other systems, and calling external functions from CLIPS. CLIPS was designed to allow both kinds of integration.


Using CLIPS as an embedded application allows the easy integration of CLIPS with existing systems. This is useful in cases where the expert system is a small part of a larger task or needs to share data with other functions. In these situations, CLIPS can be called as a subroutine and information may be passed to and from CLIPS. Em­bedded applications are discussed in the Advanced Programming Guide.


It also may be useful to call external functions while executing a CLIPS construct or from the top level of the interactive interface. CLIPS variables or literal values may be passed to an external function, and functions may return val­ues to CLIPS. The easy addition of external functions allows CLIPS to be extended or customized in almost any way. The Advanced Programming Guide describes how to integrate CLIPS with functions or systems written in C as well as in other lan­guages.

2.2 Reference Manual Syntax

The terminology used throughout this manual to describe the CLIPS syntax is fairly com­mon to computer reference manuals. Plain words or characters, particularly paren­theses, are to be typed exactly as they appear. Bolded words or characters, however, represent a verbal description of what is to be entered. Sequences of words enclosed in single angle brackets (called terms or non terminal symbols), such as <string>, represent a single entity of the named class of items to be supplied by the user. A non terminal symbol followed by a *, represents zero or more entities of the named class of items which must be supplied by the user. A non terminal symbol followed by a +, represents one or more entities of the named class of items which must be supplied by the user. A * or + by itself is to be typed as it appears. Vertical and horizontal ellipsis (three dots arranged respectively vertically and horizontally) are also used between non terminal symbols to indicate the occurrence of one or more entities. A term enclosed within square brackets, such as [<comment>], is optional (i.e. it may or may not be included). Vertical bars indicate a choice between multiple terms. White spaces (tabs, spaces, carriage re­turns) are used by CLIPS only as delimiters between terms and are ignored otherwise (unless inside double quotes). The ::= symbol is used to indicate how a non terminal symbol can be replaced. For example, the following syntax description indicates that a <lexeme> can be replaced with either a <symbol> or a <string>.


<lexeme> ::= <symbol> | <string>


A complete BNF listing for CLIPS constructs along with some commonly used replacements for non terminal symbols are listed in appendix I.

2.3 Basic Programming Elements

CLIPS provides three basic elements for writing programs: primitive data types, functions for manipulating data, and constructs for adding to a knowledge base.

2.3.1 Data Types

CLIPS provides eight primitive data types for representing information. These types are float, integer, symbol, string, external address, fact address, instance name and instance address. Numeric information can be represented using floats and integers. Symbolic information can be represented using symbols and strings.


A .ib;number; consists only of digits (0 9), a decimal point (.), a sign (+ or  ), and, optionally, an (e) for exponential notation with its corresponding sign. A number is either stored as a float; or an integer. Any number consisting of an optional sign followed by only digits is stored as an integer (represented internally by CLIPS as a C long integer). All other numbers are stored as floats (represented internally by CLIPS as a C double precision float). The number of significant digits will de­pend on the machine implementation. Roundoff errors also may occur, again depend­ing on the machine implementation. As with any computer language, care should be taken when comparing floating point values to each other or comparing integers to floating point values. Some examples of integers are


237 15 +12 -32


Some examples of floats are


237e3 15.09 +12.0 -32.3e-7


Specifically, integers use the following format:


<integer> ::= [+ | -] <digit>+


<digit> ::= 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9


Floating point numbers use the following format:


<float> ::= <integer> <exponent> |


<integer> . [exponent]


. <unsigned integer> [exponent]


<integer> . <unsigned integer> [exponent]


<unsigned-integer> ::= <digit>+


<exponent> ::= e | E <integer>


A sequence of characters which does not exactly follow the format of a number is treated as a symbol (see the next paragraph).


A symbol in CLIPS is any sequence of characters that starts with any printable ASCII character and is followed by zero or more printable ASCII characters. When a delimiter is found, the symbol is ended. The following characters act as delimiters: any non printable ASCII character (including spaces, tabs, carriage returns, and line feeds), a double quote, opening and closing parentheses “(” and “)”, an ampersand “&”, a vertical bar “|”, a less than “<”, and a tilde “~”. A semicolon “;” starts a CLIPS comment (see section 2.3.3) and also acts as a de­limiter. Delimiters may not be included in symbols with the exception of the “<“ character which may be the first character in a symbol. In addition, a symbol may not begin with either the “?” character or the “$?” sequence of characters (although a symbol may contain these characters). These characters are reserved for variables (which are discussed later in this section). CLIPS is case sensitive (i.e. uppercase letters will match only uppercase let­ters). Note that numbers are a special case of symbols (i.e. they satisfy the definition of a symbol, but they are treated as a different data type). Some simple examples of symbols are


foo Hello B76-HI bad_value


127A 456-93-039 @+=-% 2each


A string is a set of characters that starts with a double quote (“) and is followed by zero or more printable characters. A string ends with double quotes. Double quotes may be embedded within a string by placing a backslash (\) in front of the character. A backslash may be embedded by placing two consecutive back­slash characters in the string. Some examples are


“foo” “a and b” “1 number” “a\”quote”


Note that the string “abcd“ is not the same as the symbol abcd. They both contain the same characters, but are of different types. The same holds true for the instance name [abcd].


An external address is the address of an external data structure returned by a function (written in a language such as C or Ada) that has been integrated with CLIPS. This data type can only be created by calling a function (i.e. it is not possible to specify an external address by typing the value). In the basic version of CLIPS (which has no user defined external functions), it is not possible to create this data type. External addresses are discussed in further detail in the Advanced Programming Guide;. Within CLIPS, the printed representation of an external address is


<Pointer-XXXXXX>


where XXXXXX is the external address.


A fact is a list of atomic values that are either referenced positionally (ordered facts) or by name (non ordered or template facts). Facts are referred to by index or address; section 2.4.1 gives more details. The printed format of a fact address is:


<Fact-XXX>


where XXX is the fact index.


An instance is an object that is an instantiation or specific example of a class. Objects in CLIPS are defined to be floats, integers, symbols, strings, multifield values, external addresses, fact addresses or instances of a user defined class. A user defined class is created using the defclass construct. An instance of a user defined class is created with the make instance function, and such an instance can be referred to uniquely by address. Within the scope of a module (see section 10.5.1), an instance can also be uniquely referred to by name. All of these definitions will be covered in more detail in Sections 2.4.2, 2.5.2.3, 2.6 and 9. An instance name is formed by enclosing a symbol within left and right brackets. Thus, pure symbols may not be surrounded by brackets. If the CLIPS Object Oriented Language (COOL) is not included in a particular CLIPS configuration, then brackets may be wrapped around symbols. Some examples of instance names are:


[pump-1] [foo] [+++] [123-890]


Note that the brackets are not part of the name of the instance; they merely indicate that the enclosed symbol is an instance name. An instance address can only be obtained by binding the return value of a function called instance address or by binding a variable to an instance matching an object pattern on the LHS of a rule (i.e., it is not possible to specify an instance address by typing the value). A reference to an instance of a user defined class can either be by name or address; instance addresses should only be used when speed is critical. Within CLIPS, the printed representation of an instance address is


<Instance-XXX>


where XXX is the name of the instance.


In CLIPS, a placeholder that has a value (one of the primitive data types) is referred to as a field. The primitive data types are referred to as single field values. A constant is a non varying single field value directly expressed as a series of characters (which means that external addresses, fact addresses and instance addresses cannot be expressed as constants because they can only be obtained through function calls and variable bindings). A multifield value is a sequence of zero or more single field values. When displayed by CLIPS, multifield values are enclosed in parentheses. Collectively, single and multifield values are referred to as values. Some examples of multifield values are


(a) (1 bar foo) () (x 3.0 “red” 567)


Note that the multifield value (a) is not the same as the single field value a. Multifield values are created either by calling functions which return multifield values, by using wildcard arguments in a deffunction, object message handler, or method, or by binding variables during the pattern matching process for rules. In CLIPS, a variable is a symbolic location that is used to store values. Variables are used by many of the CLIPS constructs (such as defrule, deffunction, defmethod, and defmessage handler) and their usage is explained in the sections describing each of these constructs.

2.3.2 Functions

A function in CLIPS is a piece of executable code identified by a specific name which returns a useful value or performs a useful side effect (such as displaying information). Throughout the CLIPS documentation, the word function is generally used to refer only to functions which return a value (whereas commands and actions are used to refer to functions which have a side effect but generally do not return a value).


There are several types of functions. User defined functions and system defined functions are pieces of code that have been written in an external language (such as C, FORTRAN, or Ada) and linked with the CLIPS environment. System defined functions are those functions that have been defined internally by the CLIPS environment. User defined functions are functions that have been defined externally of the CLIPS environment. A complete list of system defined functions can be found in appendix J.


The deffunction construct allows users to define new functions directly in the CLIPS environment using CLIPS syntax. Functions defined in this manner appear and act like other functions, however, instead of being directly executed (as code written in an external language would be) they are interpreted by the CLIPS environment. Deffunctions are also discussed in section 2.5.2.1 in the context of procedural knowledge representation.


Generic functions can be defined using the defgeneric and defmethod constructs. Generic functions allow different pieces of code to be executed depending upon the arguments passed to the generic function. Thus, a single function name can be overloaded with more than one piece of code. Generic functions are also discussed in section 2.5.2.2 in the context of procedural knowledge representation.


Function calls in CLIPS use a prefix notation – the arguments to a function always appear after the function name. Function calls begin with a left parenthesis, followed by the name of the function, then the arguments to the function follow (each argument separated by one or more spaces). Arguments to a function can be primitive data types, variables, or another function call. The function call is then closed with a right parenthesis. Some examples of function calls using the addition (+) and multiplication (*) functions are shown following.


(+ 3 4 5)

(* 5 6.0 2)

(+ 3 (* 8 9) 4)

(* 8 (+ 3 (* 2 3 4) 9) (* 3 4))


While a function refers to a piece of executable code identified by a specific name, an expression refers to a function which has its arguments specified (which may or may not be functions calls as well). Thus the previous examples are expressions which make calls to the * and + functions.

2.3.3 Constructs

Several defining constructs appear in CLIPS: defmodule, defrule, deffacts, deftemplate, defglobal, deffunction, defclass, definstances, defmessage handler, defgeneric, and defmethod. All constructs in CLIPS are surrounded by parentheses. The construct opens with a left parenthe­sis and closes with a right parenthesis. Defining a construct differs from calling a function primarily in effect. Typically a function call leaves the CLIPS environment unchanged (with some notable exceptions such as resetting or clearing the environment or opening a file). Defining a construct, however, is explicitly intended to alter the CLIPS environment by adding to the CLIPS knowledge base. Unlike function calls, constructs never have a return value.


As with any programming language, it is highly beneficial to comment CLIPS code. All constructs (with the exception of defglobal) allow a comment directly following the construct name. Comments also can be placed within CLIPS code by using a semicolon (;). Everything from the semicolon until the next return character will be ignored by CLIPS. If the semicolon is the first character in the line, the entire line will be treated as a comment. Examples of commented code will be pro­vided throughout the reference manual. Semicolon commented text is not saved by CLIPS when loading constructs (however, the optional comment string within a construct is saved).

2.4 Data Abstraction

There are three primary formats for representing information in CLIPS: facts, objects and global variables.

2.4.1 Facts

Facts are one of the basic high level forms for representing information in a CLIPS system. Each fact represents a piece of information which has been placed in the current list of facts, called the fact list. Facts are the fundamental unit of data used by rules (see section 2.5.1).


Facts may be added to the fact list (using the assert command), removed from the fact list (using the retract command), modified (using the modify command), or duplicated (using the duplicate command) through explicit user interaction or as a CLIPS program executes;. The number of facts in the fact list and the amount of information that can be stored in a fact is limited only by the amount of memory in the computer. If a fact is asserted into the fact list that exactly matches an already existing fact, the new assertion will be ignored (however, this behavior can be changed, see sections 13.4.4 and 13.4.5).


Some commands, such as the retract, modify, and duplicate commands, require a fact to be specified. A fact can be specified either by fact index or fact address. Whenever a fact is added (or modified) it is given a unique integer index called a fact index. Fact indices start at zero and are incremented by one for each new or changed fact. Whenever a reset or clear command is given, the fact indices restart at zero. A fact may also be specified through the use of a fact address. A fact address can be obtained by capturing the return value of commands which return fact addresses (such as assert, modify, and duplicate) or by binding a variable to the fact address of a fact which matches a pattern on the LHS of a rule (see section 5.4.1.8 for details).


A fact identifier is a shorthand notation for displaying a fact. It consists of the character “f”, followed by a dash, followed by the fact index of the fact. For example, f 10 refers to the fact with fact index 10.


A fact is stored in one of two formats: ordered or non ordered.

2.4.1.1 Ordered Facts

Ordered facts consist of a symbol followed by a sequence of zero or more fields separated by spaces and delimited by an opening parenthesis on the left and a closing parenthesis on the right. The first field of an ordered fact specifies a “relation” that applied to the remaining fields in the ordered fact. For example, (father of jack bill) states that bill is the father of jack.


Some examples of ordered facts are shown following.


(the pump is on)

(altitude is 10000 feet)

(grocery-list bread milk eggs)


Fields in a non ordered fact may be of any of the primitive data types (with the exception of the first field which must be a symbol), and no restriction is placed on the ordering of fields. The following symbols are reserved and should not be used as the first field in any fact (ordered or non ordered): test, and, or, not, declare, logical, object, exists, and forall. These words are reserved only when used as a deftemplate name (whether explicitly defined or implied). These symbols may be used as slot names, however, this is not recommended.

2.4.1.2 Non ordered Facts

Ordered facts encode information positionally. To access that information, a user must know not only what data is stored in a fact but which field contains the data. Non ordered (or deftemplate) facts provide the user with the ability to abstract the structure of a fact by assign­ing names to each field in the fact. The deftemplate construct (see section 3) is used to create a template which can then be used to access fields by name. The deftemplate construct is analogous to a record or structure definition in programming languages such as Pascal and C.


The deftemplate construct allows the name of a template to be defined along with zero or more definitions of named fields or slots. Unlike ordered facts, the slots of a deftemplate fact may be constrained by type, value, and numeric range. In addition, default values can be specified for a slot. A slot consists of an opening parenthesis followed by the name of the slot, zero or more fields, and a closing parenthesis. Note that slots may not be used in an ordered fact and that positional fields may not be used in a deftemplate fact.


Deftemplate facts are distinguished from ordered facts by the first field within the fact. The first field of all facts must be a symbol, however, if that symbol corresponds to the name of a deftemplate, then the fact is a deftemplate fact. The first field of a deftemplate fact is followed by a list of zero or more slots. As with ordered facts, deftemplate facts are enclosed by an opening parenthesis on the left and a closing parenthesis on the right.

Some examples of deftemplate facts are shown following.


(client (name “Joe Brown”) (id X9345A))

(point-mass (x-velocity 100) (y-velocity -200))

(class (teacher “Martha Jones”) (#-students 30) (Room “37A”))

(grocery-list (#-of-items 3) (items bread milk eggs))


Note that the order of slots in a deftemplate fact is not important. For example the following facts are all identical:


(class (teacher “Martha Jones”) (#-students 30) (Room “37A”))

(class (#-students 30) (teacher “Martha Jones”) (Room “37A”))

(class (Room “37A”) (#-students 30) (teacher “Martha Jones”))


In contrast, note that the following ordered fact are not identical.


(class “Martha Jones” 30 “37A”)

(class 30 “Martha Jones” “37A”)

(class “37A” 30 “Martha Jones”)


The im­mediate advantages of clarity and slot order independence for deftemplate facts should be readily apparent.


In addition to being asserted and retracted, deftemplate facts can also be modified and duplicated (using the modify and duplicate commands). Modifying a fact changes a set of specified slots within that fact. Duplicating a fact creates a new fact identical to the original fact and then changes a set of specified slots within the new fact. The benefit of using the modify and duplicate commands is that slots which don’t change, don’t have to be specified.

2.4.1.3 Initial Facts

The deffacts construct allows a set of a priori or initial knowledge to be specified as a collection of facts. When the CLIPS environment is reset (using the reset command) every fact specified within a deffacts construct in the CLIPS knowledge base is added to the fact list.

2.4.2 Objects

An object in CLIPS is defined to be a symbol, a string, a floating point or integer number, a multifield value, an external address or an instance of a user defined class. Section 2.3.1 explains how to reference instances of user defined classes. Objects are described in two basic parts: properties and behavior. A classis a template for common properties and behavior of objects which are instances of that class. Some examples of objects and their classes are:


| Object (Printed Representation) | Class |

Rolls Royce SYMBOL
“Rolls Royce” STRING
8.0 FLOAT
8 INTEGER
(8.0 Rolls Royce 8 [Rolls Royce]) MULTIFIELD
<Pointer- 00CF61AB> EXTERNAL ADDRESS
[Rolls Royce] CAR (a user defined class)


Objects in CLIPS are split into two important categories: primitive types and instances of user defined classes. These two types of objects differ in the way they are referenced, created and deleted as well as how their properties are specified.


Primitive type objects are referenced simply by giving their value, and they are created and deleted implicitly by CLIPS as they are needed. Primitive type objects have no names or slots, and their classes are predefined by CLIPS. The behavior of primitive type objects is like that of instances of user defined classes, however, in that you can define message handlers and attach them to the primitive type classes. It is anticipated that primitive types will not be used often in an object oriented programming (OOP) context; the main reason classes are provided for them is for use in generic functions. Generic functions use the classes of their arguments to determine which methods to execute; sections 2.3.2, 2.5.2.2 and 8 give more detail.


An instance of a user defined class is referenced by name or address, and they are created and deleted explicitly via messages and special functions. The properties of an instance of a user defined class are expressed by a set of slots, which the object obtains from its class. As previously defined, slots are named single field or multifield values. For example, the object Rolls Royce is an instance of the class CAR. One of the slots in class CAR might be “price”, and the Rolls Royce object’s value for this slot might be $75,000.00. The behavior of an object is specified in terms of procedural code called message handlers, which are attached to the object’s class. Message handlers and manipulation of objects are described in Section 2.5.2.3. All instances of a user defined class have the same set of slots, but each instance may have different values for those slots. However, two instances which have the same set of slots do not necessarily belong to the same class, since two different classes can have identical sets of slots.


The primary difference between object slots and template (or non ordered) facts is the notion of inheritance. Inheritance allows the properties and behavior of a class to be described in terms of other classes. COOL supports multiple inheritance: a class may directly inherit slots and message handlers from more than one class. Since inheritance is only useful for slots and message handlers, it is often not meaningful to inherit from one of the primitive type classes, such as MULTIFIELD or NUMBER. This is because these classes cannot have slots and usually do not have message handlers.


Further discussion on these topics can be found in Section 2.6, and a comprehensive description of the CLIPS Object Oriented Language (COOL) can be found in Section 9.

2.4.2.1 Initial Objects

The definstances construct allows a set of a priori or initial knowledge to be specified as a collection of instances of user defined classes. When the CLIPS environment is reset (using the reset command) every instance specified within a definstances construct in the CLIPS knowledge base is added to the instance list.

2.4.3 Global Variables

The defglobal construct allows variables to be defined which are global in scope throughout the CLIPS environment. That is, a global variable can be accessed anywhere in the CLIPS environment and retains its value independent of other constructs. In contrast, some constructs (such as defrule and deffunction) allow local variables to be defined within the definition of the construct. These local variables can be referred to within the construct, but have no meaning outside the construct. A CLIPS global variable is similar to global variables found in procedural programming languages such as LISP, C and Ada. Unlike C and Ada, however, CLIPS global variables are weakly typed (they are not restricted to holding a value of a single data type).

2.5 Knowledge Representation

CLIPS provides heuristic and procedural paradigms for representing knowledge. These two paradigms are discussed in this section. Object oriented programming (which combines aspects of both data abstraction and procedural knowledge) is discussed in section 2.6.

2.5.1 Heuristic Knowledge – Rules

One of the primary methods of representing knowledge in CLIPS is a rule. Rules are used to represent heuristics, or “rules of thumb”, which specify a set of actions to be performed for a given situation. The de­veloper of an expert system defines a set of rules which collectively work together to solve a problem. A rule is composed of an antecedent and a consequent. The antecedent of a rule is also referred to as the if portion or the left hand side (LHS) of the rule. The consequent of a rule is also referred to as the then portion or the right hand side (RHS) of the rule.


The antecedent of a rule is a set of conditions (or conditional elements) which must be satisfied for the rule to be applicable. In CLIPS, the conditions of a rule are satisfied based on the existence or non existence of specified facts in the fact list or specified instances of user defined classes in the instance list. One type of condition which can be specified is a pattern. Patterns consist of a set of restrictions which are used to determine which facts or objects satisfy the condition specified by the pattern. The process of matching facts and objects to patterns is called pattern matching. CLIPS provides a mechanism, called the inference engine, which automatically matches patterns against the current state of the fact list and instance list and determines which rules are applicable.


The consequent of a rule is the set of actions to be executed when the rule is applicable. The actions of applicable rules are executed when the CLIPS inference engine is instructed to begin execution of applicable rules. If more than one rule is applicable, the inference engine uses a conflict resolution strategy to select which rule should have its actions executed. The actions of the selected rule are executed (which may affect the list of applicable rules) and then the inference engine selects another rule and executes its actions. This process continues until no applicable rules remain.


In many ways, rules can be thought of as IF THEN statements found in procedural programming languages such as C and Ada. However, the conditions of an IF THEN statement in a procedural language are only evaluated when the program flow of control is directly at the IF THEN statement. In contrast, rules act like WHENEVER THEN statements. The inference engine always keeps track of rules which have their conditions satisfied and thus rules can immediately be executed when they are applicable. In this sense, rules are similar to exception handlers found in languages such as Ada.

2.5.2 Procedural Knowledge

CLIPS also supports a procedural paradigm for representing knowledge like that of more conventional languages, such as Pascal and C. Deffunctions and generic functions allow the user to define new executable elements to CLIPS that perform a useful side effect or return a useful value. These new functions can be called just like the built in functions of CLIPS. Message handlers allow the user to define the behavior of objects by specifying their response to messages. Deffunctions, generic functions and message handlers are all procedural pieces of code specified by the user that CLIPS executes interpretively at the appropriate times. Defmodules allow a knowledge base to be partitioned.

2.5.2.1 Deffunctions

Deffunctions allow you to define new functions in CLIPS directly. In previous versions of CLIPS, the only way to have user defined functions was to write them in some external language, such as C or Ada, and then recompile and relink CLIPS with the new functions. The body of a deffunction is a series of expressions similar to the RHS of a rule that are executed in order by CLIPS when the deffunction is called. The return value of a deffunction is the value of the last expression evaluated within the deffunction. Calling a deffunction is identical to calling any other function in CLIPS. Deffunctions are covered comprehensively in Section 7.

2.5.2.2 Generic Functions

Generic functions are similar to deffunctions in that they can be used to define new procedural code directly in CLIPS, and they can be called like any other function. However, generic functions are much more powerful because they can be overloaded. A generic function will do different things depending on the types (or classes) and number of its arguments. Generic functions are comprised of multiple components called methods, where each method handles different cases of arguments for the generic function. For example, you might overload the “+” operator to do string concatenation when it is passed strings as arguments. However, the “+” operator will still perform arithmetic addition when passed numbers. There are two methods in this example: an explicit one for strings defined by the user and an implicit one which is the standard CLIPS arithmetic addition operator. The return value of a generic function is the evaluation of the last expression in the method executed. Generic functions are covered comprehensively in Section 8.

2.5.2.3 Object Message Passing

Objects are described in two basic parts: properties and behavior. Object properties are specified in terms of slots obtained from the object’s class; slots are discussed in more detail in Section 2.4.2. Object behavior is specified in terms of procedural code called message handlers which are attached to the object’s class. Objects are manipulated via message passing. For example, to cause the Rolls Royce object, which is an instance of the class CAR, to start its engine, the user must call the send function to send the message “start engine” to the Rolls Royce. How the Rolls Royce responds to this message will be dictated by the execution of the message handlers for “start engine” attached to the CAR class and any of its superclasses. The result of a message is similar to a function call in CLIPS: a useful return value or side effect.


Further discussion on message handlers can be found in Section 2.6, and a comprehensive description of the CLIPS Object Oriented Language (COOL) can be found in Section 9.

2.5.2.4 Defmodules

Defmodules allow a knowledge based to be partitioned. Every construct defined must be placed in a module. The programmer can explicitly control which constructs in a module are visible to other modules and which constructs from other modules are visible to a module. The visibility of facts and instances between modules can be controlled in a similar manner. Modules can also be used to control the flow of execution of rules. Defmodules are covered comprehensively in Section 10.

2.6 CLIPS Object Oriented Language

This section gives a brief overview of the programming elements of the CLIPS Object Oriented Language (COOL). COOL includes elements of data abstraction and knowledge representation. This section gives an overview of COOL as a whole, incorporating the elements of both concepts. Object references are discussed in Section 2.3.1, and the structure of objects is discussed in Sections 2.4.2 and 2.5.2.3. The comprehensive details of COOL are given in Section 9.

2.6.1 COOL Deviations from a Pure OOP Paradigm

In a pure OOP language, all programming elements are objects which can only be manipulated via messages. In CLIPS, the definition of an object is much more constrained: floating point and integer numbers, symbols, strings, multifield values, external addresses, fact addresses and instances of user defined classes. All objects may be manipulated with messages, except instances of user defined classes, which must be. For example, in a pure OOP system, to add two numbers together, you would send the message “add” to the first number object with the second number object as an argument. In CLIPS, you may simply call the “+” function with the two numbers as arguments, or you can define message handlers for the NUMBER class which allow you to do it in the purely OOP fashion.


All programming elements which are not objects must be manipulated in a non OOP utilizing function tailored for those programming elements. For example, to print a rule, you call the function ppdefrule; you do not send a message “print” to a rule, since it is not an object.

2.6.2 Primary OOP Features

There are five primary characteristics that an OOP system must possess: abstraction, encapsulation, inheritance, polymorphism and dynamic binding. An abstraction is a higher level, more intuitive representation for a complex concept. Encapsulation is the process whereby the implementation details of an object are masked by a well defined external interface. Classes may be described in terms of other classes by use of inheritance. Polymorphism is the ability of different objects to respond to the same message in a specialized manner. Dynamic binding is the ability to defer the selection of which specific message handlers will be called for a message until run time.


The definitions of new classes allows the abstraction of new data types in COOL. The slots and message handlers of these classes describe the properties and behavior of a new group of objects.


COOL supports encapsulation by requiring message passing for the manipulation of instances of user defined classes. An instance cannot respond to a message for which it does not have a defined message handler.

COOL allows the user to specify some or all of the properties and behavior of a class in terms of one or more unrelated superclasses. This process is called multiple inheritance. COOL uses the existing hierarchy of classes to establish a linear ordering called the class precedence list for a new class. Objects which are instances of this new class can inherit properties (slots) and behavior (message handlers) from each of the classes in the class precedence list. The word precedence implies that properties and behavior of a class first in the list override conflicting definitions of a class later in the list.


One COOL object can respond to a message in a completely different way than another object; this is polymorphism. This is accomplished by attaching message handlers with differing actions but which have the same name to the classes of these two objects respectively.


Dynamic binding is supported in that an object reference (see section 2.3.1) in a send function call is not bound until run time. For example, an instance name or variable might refer to one object at the time a message is sent and another at a later time.

2.6.3 Instance set Queries and Distributed Actions

In addition to the ability of rules to directly pattern match on objects, COOL provides a useful query system for determining, grouping and performing actions on sets of instances of user defined classes that meet user defined criteria. The query system allows you to associate instances that are either related or not. You can simply use the query system to determine if a particular association set exists, you can save the set for future reference, or you can iterate an action over the set. An example of the use of the query system might be to find the set of all pairs of boys and girls that have the same age.

Section 3   Deftemplate Construct

Ordered facts encode information positionally. To access that information, a user must know not only what data is stored in a fact but which field contains the data. Non ordered (or deftemplate) facts provide the user with the ability to abstract the structure of a fact by assign­ing names to each field found within the fact. The deftemplate construct is used to create a template which can then be used by non ordered facts to access fields of the fact by name. The deftemplate construct is analogous to a record or structure definition in programming languages such as Pascal and C.


The syntax of the deftemplate construct is:

Syntax

(deftemplate <deftemplate-name> [<comment>]

<slot-definition>*)


<slot-definition> ::= <single-slot-definition> |

<multislot-definition>


<single-slot-definition>

::= (slot <slot-name>

<template-attribute>*)


<multislot-definition>

::= (multislot <slot-name>

<template-attribute>*)


<template-attribute> ::= <default-attribute> |

<constraint-attribute>


<default-attribute>

::= (default ?DERIVE | ?NONE | <expression>*) |

(default-dynamic <expression>*)


Redefining a deftemplate will result in the previous definition being discarded. A deftemplate can not be redefined while it is being used (for example, by a fact or pattern in a rule). A deftemplate can have any number of single or multifeld slots. CLIPS always enforces the single and multifield definitions of the deftemplate. For example, it is an error to store (or match) multiple values in a single-field slot.

Example

(deftemplate object

(slot name)

(slot location)

(slot on-top-of)

(slot weight)

(multislot contents))

3.1 Slot Default Values

The <default attribute> specifies the value to be used for unspecified slots of a template fact when an assert action is performed. One of two types of default selections can be chosen: default or dynamic default.


The default attribute specifies a static default value. The specified expressions are evaluated once when the deftemplate is defined and the result is stored with the deftemplate. The result is assigned to the appropriate slot when a new template fact is asserted. If the keyword ?DERIVE is used for the default value, then a default value is derived from the constraints for the slot (see section 11.5 for more details). By default, the default attribute for a slot is (default ?DERIVE). If the keyword ?NONE is used for the default value, then a value must explicitly be assigned for a slot when an assert is performed. It is an error to assert a template fact without specifying the values for the (default ?NONE) slots.


The default dynamic attribute is a dynamic default. The specified expressions are evaluated every time a template facts is asserted, and the result is assigned to the appropriate slot.


A single field slot may only have a single value for its default. Any number of values may be specified as the default for a multifield slot (as long as the number of values satisfies the cardinality attribute for the slot).

Example

CLIPS> (clear)

CLIPS>

(deftemplate foo

(slot w (default ?NONE))

(slot x (default ?DERIVE))

(slot y (default (gensym*)))

(slot z (default-dynamic (gensym*))))

CLIPS> (assert (foo))


[TMPLTRHS1] Slot w requires a value because of its (default ?NONE) attribute.

CLIPS> (assert (foo (w 3)))

<Fact-0>

CLIPS> (assert (foo (w 4)))

<Fact-1>

CLIPS> (facts)

f-0 (foo (w 3) (x nil) (y gen1) (z gen2))

f-1 (foo (w 4) (x nil) (y gen1) (z gen3))

For a total of 2 facts.

CLIPS>

3.2 Slot Default Constraints for Pattern Matching

Single field slots that are not specified in a pattern on the LHS of a rule are defaulted to single field wildcards (?) and multifield slots are defaulted to multifield wildcards ($?).

3.3 Slot Value Constraint Attributes

The syntax and functionality of single and multifield constraint attributes are described in detail in Section 11. Static and dynamic constraint checking for deftemplates is supported. Static checking is performed when constructs or commands using deftemplates slots are being parsed (and the specific deftemplate associated with the construct or command can be immediately determined). Template patterns used on the LHS of a rule are also checked to determine if constraint conflicts exist among variables used in more that one slot. Errors for inappropriate values are immediately signaled. References to fact indexes made in commands such as modify and duplicate are considered to be ambiguous and are never checked using static checking. Static checking is enabled by default. This behavior can be changed using the set static constraint checking function. Dynamic checking is also supported. If dynamic checking is enabled, then new deftemplate facts have their values checked when added to the fact list. This dynamic checking is disabled by default. This behavior can be changed using the set dynamic constraint checking function. If an violation occurs when dynamic checking is being performed, then execution will be halted.

Example

(deftemplate object

(slot name

(type SYMBOL)

(default ?DERIVE))

(slot location

(type SYMBOL)

(default ?DERIVE))

(slot on-top-of

(type SYMBOL)

(default floor))

(slot weight

(allowed-values light heavy)

(default light))

(multislot contents

(type SYMBOL)

(default ?DERIVE)))

3.4 Implied Deftemplates

Asserting or referring to an ordered fact (such as in a LHS pattern) creates an “implied” deftemplate with a single implied multifield slot. The implied multifield slot’s name is not printed when the fact is printed. The implied deftemplate can be manipulated and examined identically to any user defined deftemplate (although it has no pretty print form).

Example

CLIPS> (clear)

CLIPS> (assert (foo 1 2 3))

<Fact-0>

CLIPS> (defrule yak (bar 4 5 6) ⇒)

CLIPS> (list-deftemplates)

initial-fact

foo

bar

For a total of 3 deftemplates.

CLIPS> (facts)

f-0 (foo 1 2 3)

For a total of 1 fact.

CLIPS>

Section 4   Deffacts Construct

With the deffacts construct, a list of facts can be defined which are automatically asserted whenever the reset command is performed. Facts as­serted through deffacts may be retracted or pattern matched like any other fact. The initial fact list, including any defined deffacts, is always reconstructed after a reset command.

Syntax

(deffacts <deffacts-name> [<comment>]
<RHS-pattern>*)


Redefining a currently existing deffacts causes the previous deffacts with the same name to be removed even if the new definition has errors in it. There may be multiple deffacts constructs and any number of facts (either ordered or deftemplate) may be asserted into the initial fact list by each deffacts construct.


Dynamic expressions may be included in a fact by embedding the expression directly within the fact. All such expressions are evaluated when CLIPS is reset.

Example

(deffacts startup “Refrigerator Status”
(refrigerator light on)
(refrigerator door open)

(refrigerator temp (get-temp)))


Upon startup and after a clear command, CLIPS automatically constructs the following deftemplate and deffacts.


(deftemplate initial-fact)


(deffacts initial-fact

(initial-fact))


This deffacts provides a convenient method for starting the execution of a system – Rules that are given no conditional element are automatically given a pattern which matches the (initial fact) fact. The initial fact deffacts can be treated identically as any other deffacts defined by the user.


Section 5   Defrule Construct

One of the primary methods of representing knowledge in CLIPS is a rule. A rule is a collec­tion of conditions and the actions to be taken if the conditions are met. The developer of an expert system defines the rules which describe how to solve a problem. Rules execute (or fire) based on the existence or non existence of facts or instances of user defined classes. CLIPS provides the mechanism (the inference engine) which attempts to match the rules to the cur­rent state of the system (as represented by the fact list and instance list) and applies the actions.


Throughout this section, the term pattern entity will be used to refer to either a fact or an instance of a user defined class.

5.1 Defining Rules

Rules are defined using the defrule construct.

Syntax

(defrule <rule-name> [<comment>]

[<declaration>] ; Rule Properties

<conditional-element>* ; Left-Hand Side (LHS)

<action>*) ; Right-Hand Side (RHS)

Redefining a currently existing defrule causes the previous defrule with the same name to be removed even if the new definition has errors in it. The LHS is made up of a series of conditional elements (CEs) which typically consist of pattern conditional elements (or just simply patterns) to be matched against pattern entities. An implicit and conditional element always surrounds all the patterns on the LHS. The RHS contains a list of actions to be per­formed when the LHS of the rule is sat­isfied. In addition, the LHS of a rule may also contain declarations about the rule’s properties immediately following the rule’s name and comment (see section 5.4.10 for more details). The arrow () separates the LHS from the RHS. There is no limit to the number of conditional elements or ac­tions a rule may have (other than the limitation placed by actual avail­able memory). Actions are performed sequentially if, and only if, all condi­tional elements on the LHS are satisfied.


If no conditional elements are on the LHS, the pattern CE (initial fact) or (initial object) is automatically used. If no ac­tions are on the RHS, the rule can be activated and fired but nothing will happen.


As rules are defined, they are incrementally reset. This means that CEs in newly defined rules can be satisfied by pattern entities at the time the rule is defined, in addition to pattern entities created after the rule is defined (see sections 13.1.8, 13.6.9, and 13.6.10 for more details).

Example

(defrule example-rule “This is an example of a simple rule”
(refrigerator light on)
(refrigerator door open)

(assert (refrigerator food spoiled)))

5.2 Basic Cycle Of Rule Execution

Once a knowledge base (in the form of rules) is built and the fact list and instance list is prepared, CLIPS is ready to execute rules. In a conventional language, the starting point, the stopping point, and the sequence of operations are defined explicitly by the program­mer. With CLIPS, the program flow does not need to be defined quite so explicitly. The knowledge (rules) and the data (facts and instances) are separated, and the inference engine pro­vided by CLIPS is used to apply the knowledge to the data. The basic execution cycle is as follows:


a) If the rule firing limit has been reached or there is no current focus, then execution is halted. Otherwise, the top rule on the agenda of the module which is the current focus is selected for execution. If there are no rules on that agenda, then the current focus is removed from the focus stack and the current focus becomes the next module on the focus stack. If the focus stack is empty, then execution is halted, otherwise step a is executed again. See sections 5.4.10.2, 10.6, 12.2, and 13.7 for information on the focus stack and the current focus.


b) The right hand side (RHS) actions of the selected rule are executed. The use of the return function on the RHS of a rule may remove the current focus from the focus stack (see sections 10.6 and 12.6.7). The number of rules fired is incremented for use with the rule firing limit.


c) As a result of step b, rules may be activated or deactivated. Activated rules (those rules whose conditions are currently satisfied) are placed on the agenda of the module in which they are defined. The placement on the agenda is determined by the salience of the rule and the current conflict resolution strategy (see sections 5.3, 5.4.10, 13.7.5, and 13.7.6). Deactivated rules are removed from the agenda. If the activations item is being watched (see section 13.2), then an informational message will be displayed each time a rule is activated or deactivated.


d) If dynamic salience is being used, the salience values for all rules on the agenda are reevaluated (see sections 5.4.10, 13.7.9, and 13.7.10). Repeat the cycle beginning with step a.

5.3 Conflict Resolution Strategies

The agenda is the list of all rules which have their conditions satisfied (and have not yet been executed). Each module has its own agenda. The agenda acts similar to a stack (the top rule on the agenda is the first one to be executed). When a rule is newly activated, its placement on the agenda is based (in order) on the following factors:


a) Newly activated rules are placed above all rules of lower salience and below all rules of higher salience.


b) Among rules of equal salience, the current conflict resolution strategy is used to determine the placement among the other rules of equal salience.


c) If a rule is activated (along with several other rules) by the same assertion or retraction of a fact, and steps a and b are unable to specify an ordering, then the rule is arbitrarily (not randomly) ordered in relation to the other rules with which it was activated. Note, in this respect, the order in which rules are defined has an arbitrary effect on conflict resolution (which is highly dependent upon the current underlying implementation of rules). Do not depend upon this arbitrary ordering for the proper execution of your rules.


CLIPS provides seven conflict resolution strategies: depth, breadth, simplicity, complexity, lex, mea, and random. The default strategy is depth. The current strategy can be set by using the set strategy command (which will reorder the agenda based upon the new strategy).

5.3.1 Depth Strategy

Newly activated rules are placed above all rules of the same salience. For example, given that fact a activates rule 1 and rule 2 and fact b activates rule 3 and rule 4, then if fact a is asserted before fact b, rule 3 and rule 4 will be above rule 1 and rule 2 on the agenda. However, the position of rule 1 relative to rule 2 and rule 3 relative to rule 4 will be arbitrary.

5.3.2 Breadth Strategy

Newly activated rules are placed below all rules of the same salience. For example, given that fact a activates rule 1 and rule 2 and fact b activates rule 3 and rule 4, then if fact a is asserted before fact b, rule 1 and rule 2 will be above rule 3 and rule 4 on the agenda. However, the position of rule 1 relative to rule 2 and rule 3 relative to rule 4 will be arbitrary.

5.3.3 Simplicity Strategy

Among rules of the same salience, newly activated rules are placed above all activations of rules with equal or higher specificity. The specificity of a rule is determined by the number of comparisons that must be performed on the LHS of the rule. Each comparison to a constant or previously bound variable adds one to the specificity. Each function call made on the LHS of a rule as part of the :, =, or test conditional element adds one to the specificity. The boolean functions and, or, and not do not add to the specificity of a rule, but their arguments do. Function calls made within a function call do not add to the specificity of a rule. For example, the following rule


(defrule example

(item ?x ?y ?x)

(test (and (numberp ?x) (> ?x (+ 10 ?y)) (< ?x 100)))

⇒)


has a specificity of 5. The comparison to the constant item, the comparison of ?x to its previous binding, and the calls to the numberp, <, and > functions each add one to the specificity for a total of 5. The calls to the and and + functions do not add to the specificity of the rule.

5.3.4 Complexity Strategy

Among rules of the same salience, newly activated rules are placed above all activations of rules with equal or lower specificity.

5.3.5 LEX Strategy

Among rules of the same salience, newly activated rules are placed using the OPS5 strategy of the same name. First the recency of the pattern entities that activated the rule is used to determine where to place the activation. Every fact and instance is marked internally with a “time tag” to indicate its relative recency with respect to every other fact and instance in the system. The pattern entities associated with each rule activation are sorted in descending order for determining placement. An activation with a more recent pattern entities is placed before activations with less recent pattern entities. To determine the placement order of two activations, compare the sorted time tags of the two activations one by one starting with the largest time tags. The comparison should continue until one activation’s time tag is greater than the other activation’s corresponding time tag. The activation with the greater time tag is placed before the other activation on the agenda.


If one activation has more pattern entities than the other activation and the compared time tags are all identical, then the activation with more time tags is placed before the other activation on the agenda. If two activations have the exact same recency, the activation with the higher specificity is placed above the activation with the lower specificity. Unlike OPS5, the not conditional elements in CLIPS have pseudo time tags which are used by the LEX conflict resolution strategy. The time tag of a not CE is always less than the time tag of a pattern entity, but greater than the time tag of a not CE that was instantiated after the not CE in question.


As an example, the following six activations have been listed in their LEX ordering (where the comma at the end of the activation indicates the presence of a not CE). Note that a fact’s time tag is not necessarily the same as it’s index (since instances are also assigned time tags), but if one fact’s index is greater than another facts’s index, then it’s time tag is also greater. For this example, assume that the time tags and indices are the same.


rule-6: f-1,f-4

rule-5: f-1,f-2,f-3,

rule-1: f-1,f-2,f-3

rule-2: f-3,f-1

rule-4: f-1,f-2,

rule-3: f-2,f-1


Shown following are the same activations with the fact indices sorted as they would be by the LEX strategy for comparison.


rule-6: f-4,f-1

rule-5: f-3,f-2,f-1,

rule-1: f-3,f-2,f-1

rule-2: f-3,f-1

rule-4: f-2,f-1,

rule-3: f-2,f-1

5.3.6 MEA Strategy

Among rules of the same salience, newly activated rules are placed using the OPS5 strategy of the same name. First the time tag of the pattern entity associated with the first pattern is used to determine where to place the activation. An activation thats first pattern’s time tag is greater than another activations first pattern’s time tag is placed before the other activation on the agenda. If both activations have the same time tag associated with the first pattern, then the LEX strategy is used to determine placement of the activation. Again, as with the CLIPS LEX strategy, negated patterns have pseudo time tags.


As an example, the following six activations have been listed in their MEA ordering (where the comma at the end of the activation indicates the presence of a negated pattern).


rule-2: f-3,f-1

rule-3: f-2,f-1

rule-6: f-1,f-4

rule-5: f-1,f-2,f-3,

rule-1: f-1,f-2,f-3

rule-4: f-1,f-2,

5.3.7 Random Strategy

Each activation is assigned a random number which is used to determine its placement among activations of equal salience. This random number is preserved when the strategy is changed so that the same ordering is reproduced when the random strategy is selected again (among activations that were on the agenda when the strategy was originally changed).

5.4 LHS Syntax

This section describes the syntax used on the LHS of a rule. The LHS of a CLIPS rule is made up of a series of conditional elements (CEs) that must be satisfied for the rule to be placed on the agenda. There are eight types of conditional elements: pattern CEs, test CEs, and CEs, or CEs, not CEs, exists CEs, forall CEs, and logical CEs. The pattern CE is the most basic and commonly used conditional element. Pattern CEs contain constraints which are used to determine if any pattern entities (facts or instances) satisfy the pattern. The test CE is used to evaluate expressions as part of the pattern matching process. The and CE is used to specify that an entire group of CEs must all be satisfied. The or CE is used to specify that only one of a group of CEs must be satisfied. The not CE is used to specify that a CE must not be satisfied. The exists CE is used to test for the occurence of at least one partial match for a set of CEs. The forall CE is used to test that a set of CEs is satisfied for every partial match of a specified CE. Finally, the logical CE allows assertions of facts and the creation of instances on the RHS of a rule to be logically dependent upon pattern entities matching patterns on the LHS of a rule (truth maintenance).


Syntax

<conditional-element> ::= <pattern-CE> |

<assigned-pattern-CE> |

<not-CE> |

<and-CE> |

<or-CE> |

<logical-CE> |

<test-CE> |

<exists-CE> |

<forall-CE>

5.4.1 Pattern Conditional Element

Pattern conditional elements consist of a collection of field constraints, wildcards, and variables which are used to constrain the set of facts or instances which match the pattern CE. A pattern CE is satisfied by each and every pattern entity that satisfies its constraints. Field constraints are a set of constraints that are used to test a single field or slot of a pattern entity. A field constraint may consist of only a single literal constraint:literal;, however, it may also consist of several constraints connected together. In addition to literal constraints, CLIPS provides three other types of constraints: connective constraints, predicate constraints, and return value constraints. Wildcards are used within pattern CEs to indicate that a single field or group of fields can be matched by anything. Variables are used to store the value of a field so that it can be used later on the LHS of a rule in other conditional elements or on the RHS of a rule as an argument to an action.


The first field of any pattern must be a symbol and can not use any other constraints. This first field is used by CLIPS to determine if the pattern applies to an ordered fact, a template fact, or an instance. The symbol object is reserved to indicate an object pattern. Any other symbol used must correspond to a deftemplate name (or an implied deftemplate will be created). Slot names must also be symbols and cannot contain any other constraints.


For object and deftemplate patterns, a single field slot can only contain one field constraint and that field constraint must only be able to match a single field (no multifield wildcards or variables). A multifield slot can contain any number of field constraints.


The examples and syntax shown in the following sections will be for ordered and deftemplate fact patterns. Section 5.4.1.7 will discuss differences between deftemplate patterns and object patterns. The following constructs are used by the examples.


(deffacts data-facts

(data 1.0 blue “red”)

(data 1 blue)

(data 1 blue red)

(data 1 blue RED)

(data 1 blue red 6.9))


(deftemplate person

(slot name)

(slot age)

(multislot friends))


(deffacts people

(person (name Joe) (age 20))

(person (name Bob) (age 20))

(person (name Joe) (age 34))

(person (name Sue) (age 34))

(person (name Sue) (age 20)))

5.4.1.1 Literal Constraints

The most basic constraint which can be used in a pattern CE is one which precisely defines the exact value that will match a field. This is called a literal constraint. A literal pattern CE consists entirely of constants such as floats, integers, symbols, strings, and instance names. It does not contain any variables or wildcards. All constraints in a literal pattern must be matched exactly by all fields of a pattern entity.


Syntax

An ordered pattern conditional element containing only literals has the following basic syntax:


(<constant-1> … <constant-n>)


A deftemplate pattern conditional element containing only literals has the following basic syntax:


(<deftemplate-name> (<slot-name-1> <constant-1>)



(<slot-name-n> <constant-n>))

Example 1

This example utilizes the data facts deffacts shown in section 5.4.1.


CLIPS> (clear)

CLIPS> (defrule find-data (data 1 blue red) ⇒)

CLIPS> (reset)

CLIPS> (agenda)

0 find-data: f-3

For a total of 1 activation.

CLIPS> (facts)

f-0 (initial-fact)

f-1 (data 1.0 blue “red”)

f-2 (data 1 blue)

f-3 (data 1 blue red)

f-4 (data 1 blue RED)

f-5 (data 1 blue red 6.9)

For a total of 6 facts.

CLIPS>

Example 2

This example utilizes the person deftemplate and people deffacts shown in section 5.4.1.


CLIPS> (clear)

CLIPS>

(defrule Find-Bob

(person (name Bob) (age 20))

⇒)

CLIPS>

(defrule Find-Sue

(person (age 34) (name Sue))

⇒)

CLIPS> (reset)

CLIPS> (agenda)

0 Find-Sue: f-4

0 Find-Bob: f-2

For a total of 2 activations.

CLIPS> (facts)

f-0 (initial-fact)

f-1 (person (name Joe) (age 20) (friends))

f-2 (person (name Bob) (age 20) (friends))

f-3 (person (name Joe) (age 34) (friends))

f-4 (person (name Sue) (age 34) (friends))

f-5 (person (name Sue) (age 20) (friends))

For a total of 6 facts.

CLIPS>

5.4.1.2 Wildcards Single  and Multifield

CLIPS has two wildcard symbols that may be used to match fields in a pat­tern. CLIPS in­terprets these wildcard symbols as standing in place of some part of a pattern entity. The single field wild­card, denoted by a question mark character (?), matches any value stored in exactly one field in the pattern entity. The multifield wildcard, denoted by a dollar sign followed by a question mark ($?), matches any value in zero or more fields in a pattern entity. Single field and multifield wildcards may be combined in a single pattern in any combination. It is illegal to use a multifield wildcard in a single field slot of a deftemplate or object pattern. By default, an unspecified single field slot in a deftemplate/object pattern is matched against an implied single field wildcard. Similarly, an unspecified multifield slot in a deftemplate/object pattern is matched against an implied multifield wildcard.


Syntax

An ordered pattern conditional element containing only literals and wildcards has the following basic syntax:


(<constraint-1> … <constraint-n>)


where


<constraint> ::= <constant> | ? | $?


A deftemplate pattern conditional element containing only literals and wildcards has the following basic syntax:


(<deftemplate-name> (<slot-name-1> <constraint-1>)



(<slot-name-n> <constraint-n>))

Example 1

This example utilizes the data facts deffacts shown in section 5.4.1.


CLIPS> (clear)

CLIPS>

(defrule find-data

(data ? blue red $?)

⇒)

CLIPS> (reset)

CLIPS> (agenda)

0 find-data: f-5

0 find-data: f-3

For a total of 2 activations.

CLIPS> (facts)

f-0 (initial-fact)

f-1 (data 1.0 blue “red”)

f-2 (data 1 blue)

f-3 (data 1 blue red)

f-4 (data 1 blue RED)

f-5 (data 1 blue red 6.9)

For a total of 6 facts.

CLIPS>

Example 2

This example utilizes the person deftemplate and people deffacts shown in section 5.4.1.


CLIPS> (clear)

CLIPS>

(defrule match-all-persons

(person)

⇒)

CLIPS> (reset)

CLIPS> (agenda)

0 match-all-persons: f-5

0 match-all-persons: f-4

0 match-all-persons: f-3

0 match-all-persons: f-2

0 match-all-persons: f-1

For a total of 5 activations.

CLIPS> (facts)

f-0 (initial-fact)

f-1 (person (name Joe) (age 20) (friends))

f-2 (person (name Bob) (age 20) (friends))

f-3 (person (name Joe) (age 34) (friends))

f-4 (person (name Sue) (age 34) (friends))

f-5 (person (name Sue) (age 20) (friends))

For a total of 6 facts.

CLIPS>


Multifield wildcard and literal constraints can be combined to yield some powerful pattern matching capabilities. A pattern to match all of the facts that have the symbol YELLOW in any field (other than the first) could be written as


(data $? YELLOW $?)


Some examples of what this pattern would match are


(data YELLOW blue red green)

(data YELLOW red)

(data red YELLOW)

(data YELLOW)

(data YELLOW data YELLOW)


The last fact will match twice since YELLOW appears twice in the fact. The use of multifield wildcards should be confined to cases of patterns in which the single field wildcard cannot create a pattern that satisfies the match required, since the multifield wildcard produces every possible match combination that can be derived from a pattern entity. This derivation of matches requires a significant amount of time to perform when compared to the time needed to perform a single field match.

5.4.1.3 Variables Single  and Multifield

Wildcard symbols replace portions of a pattern and accept any value. The value of the field being replaced may be captured in a variable for comparison, display, or other manipulations. This is done by directly following the wildcard symbol with a variable name.


Syntax

Expanding on the syntax definition given in section 5.4.1.2 now gives:


<constraint> ::= <constant> | ? | $? |

<single-field-variable> |

<multifield-variable>


<single-field-variable> ::= ?<variable-symbol>


<multifield-variable> ::= $?<variable-symbol>


where <variable symbol> is similar to a symbol, except that it must start with an alphabetic char­acter. Double quotes are not allowed as part of a variable name; i.e. a string cannot be used for a variable name. The rules for pattern matching are similar to those for wildcard symbols. On its first appearance, a variable acts just like a wildcard in that it will bind to any value in the field(s). However, later appearances of the variable require the field(s) to match the binding of the variable. The binding will only be true within the scope of the rule in which it occurs. Each rule has a private list of variable names with their associated values; thus, variables are local to a rule. Bound vari­ables can be passed to external functions. The $ operator has special significance on the LHS as a pattern matching operator to indicate that zero or more fields need to be matched. In other places (such as the RHS of a rule), the $ in front of a variable indicates that sequence expansion should take place before calling the function. Thus, when passed as parameters in function calls (either on the LHS or RHS of a rule), multifield variables should not be preceded by the $ (unless sequence expansion is desired). All other uses of a multifield variable on the LHS of a rule, however, should use the $. It is illegal to use a multifield variable in a single field slot of a deftemplate/object pattern.

Example 1

CLIPS> (clear)

CLIPS> (reset)

CLIPS> (assert (data 2 blue green)

(data 1 blue)

(data 1 blue red))

<Fact-3>

CLIPS> (facts)

f-0 (initial-fact)

f-1 (data 2 blue green)

f-2 (data 1 blue)

f-3 (data 1 blue red)

For a total of 4 facts.

CLIPS>

(defrule find-data-1

(data ?x ?y ?z)

(printout t ?x ” : “ ?y ” : “ ?z crlf))

CLIPS> (run)

1 : blue : red

2 : blue : green

CLIPS>

Example 2

CLIPS> (reset)

CLIPS> (assert (data 1 blue)

(data 1 blue red)

(data 1 blue red 6.9))

<Fact-3>

CLIPS> (facts)

f-0 (initial-fact)

f-1 (data 1 blue)

f-2 (data 1 blue red)

f-3 (data 1 blue red 6.9)

For a total of 4 facts.

CLIPS>

(defrule find-data-1

(data ?x $?y ?z)

(printout t ”?x = “ ?x crlf

”?y = “ ?y crlf

”?z = “ ?z crlf

”——“ crlf))

CLIPS> (run)

?x = 1

?y = (blue red)

?z = 6.9

------

?x = 1

?y = (blue)

?z = red

------

?x = 1

?y = ()

?z = blue

------

CLIPS>


Once the initial binding of a variable occurs, all references to that variable have to match the value that the first binding matched. This applies to both single  and multi­field variables. It also applies across patterns.

Example 3

CLIPS> (clear)

CLIPS>

(deffacts data

(data red green)

(data purple blue)

(data purple green)

(data red blue green)

(data purple blue green)

(data purple blue brown))

CLIPS>

(defrule find-data-1

(data red ?x)

(data purple ?x)

⇒)

CLIPS>

(defrule find-data-2

(data red $?x)

(data purple $?x)

⇒)

CLIPS> (reset)

CLIPS> (facts)

f-0 (initial-fact)

f-1 (data red green)

f-2 (data purple blue)

f-3 (data purple green)

f-4 (data red blue green)

f-5 (data purple blue green)

f-6 (data purple blue brown)

For a total of 7 facts.

CLIPS> (agenda)

0 find-data-2: f-4,f-5

0 find-data-1: f-1,f-3

0 find-data-2: f-1,f-3

For a total of 3 activations.

CLIPS>

5.4.1.4 Connective Constraints

Three connective constraints are available for connecting individual constraints and variables to each other. These are the & (and), | (or), and ~ (not) connective constraints. The & constraint is satisfied if the two adjoining constraints are satisfied. The | constraint is satisfied if either of the two adjoining constraints is satisfied. The ~ constraint is satisfied if the following constraint is not satisfied. The connective constraints can be com­bined in almost any manner or number to constrain the value of specific fields while pattern matching. The ~ constraint has highest precedence, followed by the & constraint, followed by the | constraint. Otherwise, evaluation of multiple constraints can be considered to occur from left to right. There is one exception to the precedence rules which applies to the binding occurrence of a variable. If the first constraint is a variable followed by an & connective constraint, then the first constraint is treated as a separate constraint which also must be satisified. Thus the constraint ?x&red|blue is treated like ?x&(red|blue) rather than (?x&red)|blue as the normal precedence rules would indicate.

Basic Syntax

Connective constraints have the following basic syntax:


<term-1>&<term-2> … &<term-3>


<term-1>|<term-2> … |<term-3>


~<term>


where <term> could be a single field variable, multifield variable, constant, or connected constraint.


Syntax

Expanding on the syntax definition given in section 5.4.1.3 now gives:


<constraint> ::= ? | $? | <connected-constraint>


<connected-constraint>

::= <single-constraint> |

<single-constraint> & <connected-constraint> |

<single-constraint> | <connected-constraint>


<single-constraint> ::= <term> | ~<term>


<term> ::= <constant> |

<single-field-variable> |

<multifield-variable>


The &constraint typically is used only in conjunction with other constraints or variable bindings. Notice that connective constraints may be used together and/or with variable bindings. If the first term of a connective constraint is the first occurrence of a variable name, then the field will be constrained only by the remaining field constraints. The variable will be bound to the value of the field. If the variable has been bound previously, it is considered an additional con­straint along with the remaining field constraints; i.e., the field must have the same value already bound to the variable and must satisfy the field constraints.

Example 1

CLIPS> (clear)

CLIPS> (deftemplate data-B (slot value))

CLIPS>

(deffacts AB

(data-A green)

(data-A blue)

(data-B (value red))

(data-B (value blue)))

CLIPS>

(defrule example1-1

(data-A ~blue)

⇒)

CLIPS>

(defrule example1-2

(data-B (value ~red&~green))

⇒)

CLIPS>

(defrule example1-3

(data-B (value green|red))

⇒)

CLIPS> (reset)

CLIPS> (facts)

f-0 (initial-fact)

f-1 (data-A green)

f-2 (data-A blue)

f-3 (data-B (value red))

f-4 (data-B (value blue))

For a total of 5 facts.

CLIPS> (agenda)

0 example1-2: f-4

0 example1-3: f-3

0 example1-1: f-1

For a total of 3 activations.

CLIPS>

Example 2

CLIPS> (clear)

CLIPS> (deftemplate data-B (slot value))

CLIPS>

(deffacts B

(data-B (value red))

(data-B (value blue)))

CLIPS>

(defrule example2-1

(data-B (value ?x&~red&~green))

(printout t ”?x in example2-1 = “ ?x crlf))

CLIPS>

(defrule example2-2

(data-B (value ?x&green|red))

(printout t ”?x in example2-2 = “ ?x crlf))

CLIPS> (reset)

CLIPS> (run)

?x in example2-1 = blue

?x in example2-2 = red

CLIPS>

Example 3

CLIPS> (clear)

CLIPS> (deftemplate data-B (slot value))

CLIPS>

(deffacts AB

(data-A green)

(data-A blue)

(data-B (value red))

(data-B (value blue)))

CLIPS>

(defrule example3-1

(data-A ?x&~green)

(data-B (value ?y&~?x))

⇒)

CLIPS>

(defrule example3-2

(data-A ?x)

(data-B (value ?x&green|blue))

⇒)

CLIPS>

(defrule example3-3

(data-A ?x)

(data-B (value ?y&blue|?x))

⇒)

CLIPS> (reset)

CLIPS> (facts)

f-0 (initial-fact)

f-1 (data-A green)

f-2 (data-A blue)

f-3 (data-B (value red))

f-4 (data-B (value blue))

For a total of 5 facts.

CLIPS> (agenda)

0 example3-3: f-1,f-4

0 example3-3: f-2,f-4

0 example3-2: f-2,f-4

0 example3-1: f-2,f-3

For a total of 4 activations.

CLIPS>

5.4.1.5 Predicate Constraints

Sometimes it becomes necessary to constrain a field based upon the truth of a given boolean expression. CLIPS allows the use of a predicate constraint to restrict a field in this manner. The predicate constraint allows a predicate function (one returning the symbol FALSE for unsatisfied and a non FALSE value for satisfied) to be called during the pattern matching process. If the predicate function returns a non FALSE value, the constraint is satisfied. If the predicate function returns the symbol FALSE, the constraint is not satisfied. A predicate constraint is invoked by following a colon with an appropriate function call to a predicate function. Typically, predicate constraints are used in conjunction with a connective constraint and a variable binding (i.e. you have to bind the variable to be tested and then connect it to the predicate constraint).

Basic Syntax

:<function-call>


Syntax

Expanding on the syntax definition given in section 5.4.1.4 now gives:


<term> ::= <constant> |

<single-field-variable> |

<multifield-variable> |

:<function-call>


Multiple predicate constraints may be used to constrain a single field. Several predicate functions are provided by CLIPS (see section 12.2). Users also may develop their own predicate functions.

Example 1

CLIPS> (clear)

CLIPS>

(defrule example-1

(data ?x&:(numberp ?x))

⇒)

CLIPS> (assert (data 1) (data 2) (data red))

<Fact-2>

CLIPS> (agenda)

0 example-1: f-1

0 example-1: f-0

For a total of 2 activations.

CLIPS>

Example 2

CLIPS> (clear)

CLIPS>

(defrule example-2

(data ?x&~:(symbolp ?x))

⇒)

CLIPS> (assert (data 1) (data 2) (data red))

<Fact-2>

CLIPS> (agenda)

0 example-2: f-1

0 example-2: f-0

For a total of 2 activations.

CLIPS>

Example 3

CLIPS> (clear)

CLIPS>

(defrule example-3

(data ?x&:(numberp ?x)&:(oddp ?x))

⇒)

CLIPS> (assert (data 1) (data 2) (data red))

<Fact-2>

CLIPS> (agenda)

0 example-3: f-0

For a total of 1 activation.

CLIPS>

Example 4

CLIPS> (clear)

CLIPS>

(defrule example-4

(data ?y)

(data ?x&:(> ?x ?y))

⇒)

CLIPS> (assert (data 3) ; f-0

(data 5) ; f-1

(data 9)) ; f-2

<Fact-2>

CLIPS> (agenda)

0 example-4: f-0,f-2

0 example-4: f-1,f-2

0 example-4: f-0,f-1

For a total of 3 activations.

CLIPS>

Example 5

CLIPS> (clear)

CLIPS>

(defrule example-5

(data $?x&:(> (length$ ?x) 2))

⇒)

CLIPS> (assert (data 1) ; f-0

(data 1 2) ; f-1

(data 1 2 3)) ; f-2

<Fact-2>

CLIPS> (agenda)

0 example-5: f-2

For a total of 1 activation.

CLIPS>

5.4.1.6 Return Value Constraints

It is possible to use the return value of an external function to constrain the value of a field. The return value constraint (=) allows the user to call external functions from inside a pat­tern. (This constraint is different from the com­parison function which uses the same symbol. The difference can be determined from context.) The return value must be one of the primitive data types. This value is incorporated directly into the pattern at the position at which the function was called as if it were a literal constraint, and any matching pat­terns must match this value as though the rule were typed with that value. Note that the function is evaluated each time the constraint is checked (not just once).

Basic Syntax

=<function-call>


Syntax

Expanding on the syntax definition given in section 5.4.1.5 now gives:


<term> ::= <constant> |

<single-field-variable> |

<multifield-variable> |

:<function-call> |

=<function-call>

Example 1

CLIPS> (clear)

CLIPS> (deftemplate data (slot x) (slot y))

CLIPS>

(defrule twice

(data (x ?x) (y =(* 2 ?x)))

⇒)

CLIPS> (assert (data (x 2) (y 4)) ; f-0

(data (x 3) (y 9))) ; f-1

<Fact-1>

CLIPS> (agenda)

0 twice: f-0

For a total of 1 activation.

CLIPS>

Example 2

CLIPS> (clear)

CLIPS>

(defclass DATA (is-a USER)

(role concrete) (pattern-match reactive)

(slot x (create-accessor write)))

CLIPS>

(defrule return-value-example-2

(object (is-a DATA)

(x ?x1))

(object (is-a DATA)

(x ?x2&=(+ 5 ?x1)|=(- 12 ?x1)))

⇒)

CLIPS> (make-instance of DATA (x 4))

[gen1]

CLIPS> (make-instance of DATA (x 9))

[gen2]

CLIPS> (make-instance of DATA (x 3))

[gen3]

CLIPS> (agenda)

0 return-value-example-2: [gen3],[gen2]

0 return-value-example-2: [gen2],[gen3]

0 return-value-example-2: [gen1],[gen2]

For a total of 3 activations.

CLIPS>

5.4.1.7 Pattern Matching with Object Patterns

Instances of user defined classes in COOL can be pattern matched on the left hand side of rules. Patterns can only match objects for which the object’s most specific class is defined before the pattern and which are in scope for the current module. Any classes which could have objects which match the pattern cannot be deleted or changed until the pattern is deleted. Even if a rule is deleted by its RHS, the classes bound to its patterns cannot be changed until after the RHS finishes executing.


When an instance is created or deleted, all patterns applicable to that object are updated. However, when a slot is changed, only those patterns which explicitly match on that slot are affected. Thus, one could use logical dependencies to hook to a change to a particular slot (rather than a change to any slot, which is all that is possible with deftemplates).


Changes to non reactive slots or instances of non reactive classes (see sections 9.3.2.2 and 9.3.3.7) will have no effect on rules. Also Rete network activity will not be immediately apparent after changes to slots are made if pattern matching is being delayed through the use of the make instance, i.initialize instance;, i.modify instance;, i.message modify instance;, i.duplicate instance;, i.message duplicate instance; or object pattern match delay functions.


Syntax

<object-pattern> ::= (object <attribute-constraint>*)


<attribute-constraint> ::= (is-a <constraint>) |

(name <constraint>) |

(<slot-name> <constraint>*)


The is a constraint is used for specifying class constraints such as “Is this object a member of class FOO?”. The is a constraint also encompasses subclasses of the matching classes unless specifically excluded by the pattern. The name constraint is used for specifying a specific instance on which to pattern match. The evaluation of the name constraint must be of primitive type instance name, not symbol. Multifield constraints (such as $?) cannot be used with the is a or name constraints. Other than these special cases, constraints used in object slots work similarly to constraints used in deftemplate slots. As with deftemplate patterns, slot names for object patterns must be symbols and can not contain any other constraints.

Example 1

The following rules illustrate pattern matching on an object's class.


(defrule class-match-1

(object)

⇒)


(defrule class-match-2

(object (is-a FOO))

⇒)


(defrule class-match-3

(object (is-a FOO | BAR))

⇒)


(defrule class-match-4

(object (is-a ?x))

(object (is-a ~?x))

⇒)


Rule class match 1 is satisified by all instances of any reactive class. Rule class match 2 is satisfied by all instances of class FOO. Rule class match 3 is satisfied by all instances of class FOO or BAR. Rule class match 4 will be satisfied by any two instances of mutually exclusive classes.

Example 2

The following rules illustrate pattern matching on various attributes of an object's slots.


(defrule slot-match-1

(object (width))

⇒)


(defrule slot-match-2

(object (width ?))

⇒)


(defrule slot-match-3

(object (width $?))

⇒)


Rule slot match 1 is satisfied by all instances of reactive classes that contain a reactive width slot with a zero length multifield value. Rule slot match 2 is satisfied by all instances of reactive classes that contain a reactive single or multifield width slot that is bound to a single value. Rule slot match 3 is satisfied by all instances of reactive classes that contain a reactive single or multifield width slot that is bound to any number of values. Note that a slot containing a zero length multifield value would satisfy rules slot match 1 and slot match 3, but not rule slot match 2 (because the value's cardinality is zero).

Example 3

The following rules illustrate pattern matching on the slot values of an object.


(defrule value-match-1

(object (width 10)

⇒)


(defrule value-match-2

(object (width ?x&:(> ?x 20)))

⇒)


(defrule value-match-3

(object (width ?x) (height ?x))

⇒)


Rule value match 1 is satisified by all instances of reactive classes that contain a reactive width slot with value 10. Rule value match 2 is satisfied by all instances of reactive classes that contain a reactive width slot that has a value greater than 20. Rule value match 3 is satisfied by all instances of reactive classes that contain a reactive width and height slots with the same value.

5.4.1.8 Pattern Addresses

Certain RHS actions, such as retract and unmake instance, operate on an entire pattern CE. To signify which fact or instance they are to act upon, a variable can be bound to the fact address or instance address of a pattern CE. Collectively, fact addresses and instance addresses bound on the LHS of a rule are referred to as pattern addresses.

Syntax

<assigned-pattern-CE> ::= ?<variable-symbol> <pattern-CE>


The left arrow, , is a required part of the syntax. A variable bound to a fact address or instance address can be compared to other variables or passed to external functions. Variables bound to a fact or instance address may later be used to constrain fields within a pattern CE, however, the reverse is not allowed. It is an error to bind a varible to a not CE.

Examples

(defrule dummy

(data 1)

?fact ← (dummy pattern)

(retract ?fact))


(defrule compare-facts-1

?f1 ← (color ~red)

?f2 ← (color ~green)

(test (neq ?f1 ?f2))

(printout t “Rule fires from different facts” crlf))


(defrule compare-facts-2

?f1 ← (color ~red)

?f2 ← (color ~green&:(neq ?f1 ?f2))

(printout t “Rule fires from different facts” crlf))


(defrule print-and-delete-all-objects

?ins ← (object)

(send ?ins print)

(unmake-instance ?ins))

5.4.2 Test Conditional Element

Field constraints used within pattern CEs allow very descriptive constraints to be applied to pattern matching. Additional capability is provided with the test conditional element. The test CE is satisfied if the function call within the test CE evaluates to a non FALSE value and unsatisfied if the function call evaluates to FALSE. As with predicate constraints, the user can compare the variable bindings that already have oc­curred in any manner. Mathematical comparisons on variables (e.g., is the differ­ence between ?x and ?y greater than some value?) and complex logical or equality comparisons can be done. External functions also can be called which compare vari­ables in any way that the user desires.


Any kind of external function may be embedded within a test conditional element (or within field constraints). User defined predicate functions must take arguments as defined in the Advanced Programming Guide. Sev­eral predicate functions are provided by CLIPS (see section 12.1).

Syntax

<test-CE> ::= (test <function-call>)


Since the symbol test is used to indicate this type of conditional element, rules may not use the symbol test as the first field in a pattern CE. A test CE is evaluated when all proceeding CEs are satisfied. This means that a test CE will be evaluated more than once if the proceeding CEs can be satisfied by more than one group of pattern entities. In order to cause the reevaluation of a test CE, a pattern entity matching a CE prior to the test CE must be changed. The use of test CEs can cause additional CEs to be added to the rule. In addition, test CEs may also be automatically reordered by CLIPS. See section 5.4.9 for more details.

Example 1

This example checks to see if the difference between two numbers is greater than or equal to three:


CLIPS> (clear)

CLIPS>

(defrule example-1

(data ?x)

(value ?y)

(test (>= (abs (- ?y ?x)) 3))

⇒)

CLIPS> (assert (data 6) (value 9))

<Fact-1>

CLIPS> (agenda)

0 example-1: f-0,f-1

For a total of 1 activation.

CLIPS>

Example 2

This example checks to see if there is a positive slope between two points on a line.


CLIPS> (clear)

CLIPS>

(deffunction positive-slope

(?x1 ?y1 ?x2 ?y2)

(< 0 (/ (- ?y2 ?y1) (- ?x2 ?x1))))

CLIPS>

(defrule example-2

(point ?a ?x1 ?y1)

(point ?b ?x2 ?y2)

(test (> ?b ?a))

(test (positive-slope ?x1 ?y1 ?x2 ?y2))

⇒)

CLIPS>

(assert (point 1 4.0 7.0) (point 2 5.0 9.0))

<Fact-1>

CLIPS> (agenda)

0 example-2: f-0,f-1

For a total of 1 activation.

CLIPS>


Important Note

Because the test CE can cause the addition of the initial fact fact pattern or the initial object instance pattern to a rule, a reset command (which creates the initial fact fact and the initial object instance) must be issued for the correct operation of the test CE under all circumstances.

5.4.3 Or Conditional Element

The or conditional element allows any one of several conditional elements to activate a rule. If any of the conditional elements inside of the or CE is satisfied, then the or CE is satisfied. If all other LHS condi­tional elements are satisfied, the rule will be activated. Note that a rule will be activated for each conditional element with an or CE that is satisfied (assuming the other conditional elements of the rule are also satisfied). Any number of conditional elements may appear within an or CE. The or CE produces the identical effect of writing several rules with sim­ilar LHS’s and RHS’s.

Syntax

<or-CE> ::= (or <conditional-element>+)

Again, if more than one of the conditional elements in the or CE can be met, the rule will fire multiple times, once for each satisfied combination of conditions.

Example

(defrule system-fault
(error-status unknown)
(or (temp high)
(valve broken)

(pump (status off)))

(printout t “The system has a fault.” crlf))


Note that the above example is exactly equivalent to the following three (separate) rules:


(defrule system-fault
(error-status unknown)
(pump (status off))

(printout t “The system has a fault.” crlf))


(defrule system-fault
(error-status unknown)
(valve broken)

(printout t “The system has a fault.” crlf))


(defrule system-fault
(error-status unknown)
(temp high)

(printout t “The system has a fault.” crlf))

5.4.4 And Conditional Element

CLIPS assumes that all rules have an implicit and conditional element surrounding the conditional elements on the LHS. This means that all conditional elements on the LHS must be satisfied before the rule can be activated. An explicit and conditional element is provided to allow the mixing of and CEs and or CEs. This allows other types of conditional elements to be grouped together within or and not CEs. The and CE is satisfied if all of the CEs inside of the explicit and CE are satisfied. If all other LHS condi­tions are true, the rule will be activated. Any number of conditional elements may be placed within an and CE.

Syntax

<and-CE> ::= (and <conditional-element>+)

Example

(defrule system-flow
(error-status confirmed)
(or (and (temp high)
(valve closed))
(and (temp low)
(valve open)))

(printout t “The system is having a flow problem.” crlf))


An and CE that has a test or not CE as its first CE has the pattern (initial fact) or (initial object) added as the first CE. Note that the LHS of any rule is enclosed within an implied and CE. For example, the following rule


(defrule nothing-to-schedule

(not (schedule ?))

(printout t “Nothing to schedule.” crlf))


is converted to


(defrule nothing-to-schedule

(and (initial-fact)

(not (schedule ?)))

(printout t “Nothing to schedule.” crlf))

5.4.5 Not Conditional Element

Sometimes the lack of information is meaningful; i.e., one wishes to fire a rule if a pattern entity or other CE does not exist. The not conditional element provides this capability. The not CE is satisfied only if the conditional element contained within it is not satisfied. As with other conditional elements, any number of additional CEs may be on the LHS of the rule and field con­straints may be used within the negated pattern.

Syntax

<not-CE> ::= (not <conditional-element>)


Only one CE may be negated at a time. Multiple patterns may be negated by using multiple not CEs. Care must be taken when combining not CEs with or and and CEs; the results are not always obvi­ous! The same holds true for variable bindings within a not CE. Previously bound variables may be used freely inside of a not CE. However, variables bound for the first time within a not CE can be used only in that pattern.

Examples

(defrule high-flow-rate
(temp high)
(valve open)
(not (error-status confirmed))

(printout t “Recommend closing of valve due to high temp”

crlf))


(defrule check-valve
(check-status ?valve)
(not (valve-broken ?valve))

(printout t “Device ” ?valve ” is OK“ crlf))


(defrule double-pattern
(data red)

(not (data red ?x ?x))

(printout t “No patterns with red green green!” crlf ))


A not CE that contains a single test CE is converted such that the test CE is contained within an and CE and is preceded by the (initial fact) or (initial object) pattern. For example, the following conditional element


(not (test (> ?time-1 ?time-2)))


is converted to


(not (and (initial-fact)

(test (> ?time-1 ?time-2))))


Note that it is much simpler just to convert the test CE to the following format:


(test (not (> ?time-1 ?time-2)))


Important Note

Because the not CE can cause the addition of the initial fact fact pattern or the initial object instance pattern to a rule, a reset command (which creates the initial fact fact and the initial object instance) must be issued for the correct operation of the not CE under all circumstances.

5.4.6 Exists Conditional Element

The exists conditional element provides a mechanism for determining if a group of specified CEs is satisfied by a least one set of pattern entities.

Syntax

<exists-CE> ::= (exists <conditional-element>+)


The exists CE is implemented by replacing the exists keyword with two nested not CEs. For example, the following rule


(defrule example

(exists (a ?x) (b ?x))

⇒)


is equivalent to the rule below


(defrule example

(not (not (and (a ?x) (b ?x))))

⇒)


Because of the way the exists CE is implemented using not CEs, the restrictions which apply to CEs found within not CEs (such as binding a pattern CE to a fact address) also apply to the CEs found within an exists CE.

Example

Given the following constructs,


CLIPS> (clear)

CLIPS>

(deftemplate hero

(multislot name)

(slot status (default unoccupied)))

CLIPS>

(deffacts goal-and-heroes

(goal save-the-day)

(hero (name Death Defying Man))

(hero (name Stupendous Man))

(hero (name Incredible Man)))

CLIPS>

(defrule save-the-day

(goal save-the-day)

(exists (hero (status unoccupied)))

(printout t “The day is saved.” crlf))

CLIPS>


the following commands illustrate that even though there are three facts which can match the second CE in the save the day rule, there is only one partial match generated.


CLIPS> (reset)

CLIPS> (agenda)

0 save-the-day: f-1,

For a total of 1 activation.

CLIPS> (facts)

f-0 (initial-fact)

f-1 (goal save-the-day)

f-2 (hero (name Death Defying Man) (status unoccupied))

f-3 (hero (name Stupendous Man) (status unoccupied))

f-4 (hero (name Incredible Man) (status unoccupied))

For a total of 5 facts.

CLIPS> (matches save-the-day)

Matches for Pattern 1

f-1

Matches for Pattern 2

f-0

Matches for Pattern 3

f-2

f-3

f-4

Partial matches for CEs 1 - 2

f-1,

Activations

f-1,

CLIPS>


Important Note

The exists CE is implemented using the not CE. Because the not CE can cause the addition of the initial fact fact pattern or the initial object instance pattern to a rule, a reset command (which creates the initial fact fact and the initial object instance) must be issued for the correct operation of the exists CE under all circumstances.

5.4.7 Forall Conditional Element

The forall conditional element provides a mechanism for determining if a group of specified CEs is satisfied for every occurence of another specified CE.

Syntax

<forall-CE> ::= (forall <conditional-element>

<conditional-element>+)


The forall CE is implemented by replacing the forall keyword with combinations of not and and CEs. For example, the following rule


(defrule example

(forall (a ?x) (b ?x) (c ?x))

⇒)


is equivalent to the rule below


(defrule example

(not (and (a ?x)

(not (and (b ?x) (c ?x)))))

⇒)


Because of the way the forall CE is implemented using not CEs, the restrictions which apply to CE found within not CEs (such as binding a pattern CE to a fact address) also apply to the CEs found within an forall CE.

Example

The following rule determines if every student has passed in reading, writing, and arithmetic by using the forall CE.


CLIPS> (clear)

CLIPS>

(defrule all-students-passed

(forall (student ?name)

(reading ?name)

(writing ?name)

(arithmetic ?name))

(printout t “All students passed.” crlf))

CLIPS>


The following commands illustrate how the forall CE works in the all students passed rule. Note that initially the all students passed rule is satisfied because there are no students.


CLIPS> (reset)

CLIPS> (agenda)

0 all-students-passed: f-0,

For a total of 1 activation.

CLIPS>


After the (student Bob) fact is asserted, the rule is no longer satisfied since Bob has not passed reading, writing, and arithmetic.


CLIPS> (assert (student Bob))

<Fact-1>

CLIPS> (agenda)

CLIPS>


The rule is still not satisfied after Bob has passed reading and writing, since he still has not passed arithmetic.


CLIPS> (assert (reading Bob) (writing Bob))

<Fact-3>

CLIPS> (agenda)

CLIPS>


Once Bob has passed arithmetic, the all students passed rule is reactivated.


CLIPS> (assert (arithmetic Bob))

<Fact-4>

CLIPS> (agenda)

0 all-students-passed: f-0,

For a total of 1 activation.

CLIPS>


If a new student is asserted, then the rule is taken off the agenda, since John has not passed reading, writing, and arithmetic.


CLIPS> (assert (student John))

<Fact-5>

CLIPS> (agenda)

CLIPS>


Removing both student facts reactivates the rule again.


CLIPS> (retract 1 5)

CLIPS> (agenda)

0 all-students-passed: f-0,

For a total of 1 activation.

CLIPS>


Important Note

The forall CE is implemented using the not CE. Because the not CE can cause the addition of the initial fact fact pattern or the initial object instance pattern to a rule, a reset command (which creates the initial fact fact and the initial object instance) must be issued for the correct operation of the forall CE under all circumstances.

5.4.8 Logical Conditional Element

The logical conditional element provides a truth maintenance capability for pattern entities (facts or instances) created by rules which use the logical CE. A pattern entity created on the RHS (or as a result of actions performed from the RHS) can be made logically dependent upon the pattern entities which matched the patterns enclosed with the logical CE on the LHS of the rule. The pattern entities matching the LHS logical patterns provide logical support to the facts and instance created by the RHS of the rule. A pattern entity can be logically supported by more than one group of pattern entities from the same or different rules. If any one supporting pattern entities is removed from a group of supporting pattern entities (and there are no other supporting groups), then the pattern entity is removed.


If a pattern entity is created without logical support (e.g., from a deffacts, definstaces, as a top level command, or from a rule without any logical patterns), then the pattern entity has unconditional support. Unconditionally supporting a pattern entity removes all logical support (without causing the removal of the pattern entity). In addition, further logical support for an unconditionally supported pattern entity is ignored. Removing a rule that generated logical support for a pattern entity, removes the logical support generated by that rule (but does not cause the removal of the pattern entity if no logical support remains).

Syntax

<logical-CE> ::= (logical <conditional-element>+)


The logical CE groups patterns together exactly as the explicit and CE does. It may be used in conjunction with the and, or, and not CEs. However, only the first N patterns of a rule can have the logical CE applied to them. For example, the following rule is legal


(defrule ok

(logical (a))

(logical (b))

©

(assert (d)))


whereas the following rules are illegal


(defrule not-ok-1

(logical (a))

(b)

(logical ©)

(assert (d)))


(defrule not-ok-2

(a)

(logical (b))

(logical ©)

(assert (d)))


(defrule not-ok-3

(or (a)

(logical (b)))

(logical ©)

(assert (d)))

Example

Given the following rules,


CLIPS> (clear)

CLIPS>

(defrule rule1

(logical (a))

(logical (b))

©

(assert (g) (h)))

CLIPS>

(defrule rule2

(logical (d))

(logical (e))

(f)

(assert (g) (h)))

CLIPS>


the following commands illustrate how logical dependencies work.


CLIPS> (watch facts)

CLIPS> (watch activations)

CLIPS. (watch rules)

CLIPS> (assert (a) (b) © (d) (e) (f))

==> f-0 (a)

==> f-1 (b)

==> f-2 ©

==> Activation 0 rule1: f-0,f-1,f-2

==> f-3 (d)

==> f-4 (e)

==> f-5 (f)

==> Activation 0 rule2: f-3,f-3,f-5

<Fact-5>

CLIPS> (run)

FIRE 1 rule2: f-3,f-4,f-5 ; 1st rule adds logical support

==> f-6 (g)

==> f-7 (h)

FIRE 2 rule1: f-0,f-1,f-2 ; 2nd rule adds further support

CLIPS> (retract 1)

⇐= f-0 (a) ; Removes 1st support for (g) and (h)

CLIPS> (assert (h)) ; (h) is unconditionally supported

FALSE

CLIPS> (retract 3)

⇐= f-3 (d) ; Removes 2nd support for (g)

⇐= f-6 (g) ; (g) has no more support

CLIPS> (unwatch all)

CLIPS>


As mentioned in section 5.4.1.7, the logical CE can be used with an object pattern to create pattern entities which are logically dependent on changes to specific slots in the matching instance(s) rather than all slots. This cannot be accomplished with template facts because a change to a template fact slot actually involves the retraction of the old template fact and the assertion of a new one, whereas a change to an instance slot is done in place. The example below illustrates this behavior:


CLIPS> (clear)

CLIPS>

(defclass A (is-a USER)

(role concrete)

(pattern-match reactive)

(slot foo (create-accessor write))

(slot bar (create-accessor write)))

CLIPS>

(deftemplate A

(slot foo)

(slot bar))

CLIPS>

(defrule match-A-s

(logical (object (is-a A) (foo ?))

(A (foo ?)))

(assert (new-fact)))

CLIPS> (make-instance a of A)

[a]

CLIPS> (assert (A))

<Fact-0>

CLIPS> (watch facts)

CLIPS> (run)

==> f-1 (new-fact)

CLIPS> (send [a] put-bar 100)

100

CLIPS> (agenda)

CLIPS> (modify 0 (bar 100))

⇐= f-0 (A (foo nil) (bar nil))

⇐= f-1 (new-fact)

==> f-2 (A (foo nil) (bar 100))

<Fact-2>

CLIPS> (agenda)

0 match-A-s: [a],f-2

For a total of 1 activation.

CLIPS> (run)

==> f-3 (new-fact)

CLIPS> (send [a] put-foo 100)

⇐= f-3 (new-fact)

100

CLIPS> (agenda)

0 match-A-s: [a],f-2

For a total of 1 activation.

CLIPS> (unwatch facts)

CLIPS>

5.4.9 Automatic Addition and Reordering of LHS CEs

Under certain circumstances, CLIPS adds additional pattern CEs to rules (usually for the benefit of the pattern matching algorithm used by CLIPS). There are two default patterns used by CLIPS: the initial fact fact pattern and the initial object instance pattern. The initial fact pattern is


(initial-fact)


and the initial object pattern is


(object (is-a INITIAL-OBJECT) (name [initial-object]))

5.4.9.1 Rules Without Any LHS Pattern CEs

The initial fact pattern is added to any rule that has no patterns on its LHS (unless facts have been disabled by configuring CLIPS in which case the initial object pattern is added to the LHS of the rule). For example, the following rule


(defrule example-1

⇒)


would be changed as follows.


(defrule example-1

(initial-fact)

⇒)

5.4.9.2 Test and Not CEs as the First CE of an And CE

Test CEs and not CEs that are the first CE within an and CE have an initial fact or an initial object pattern added immediately before them. An initial fact pattern is added if the first pattern CE preceding the CE in question is a fact pattern. An initial object pattern is added if the first pattern CE preceding the CE in question is an object pattern. If there are no preceding pattern CEs, the type of pattern is determined by the succeeding pattern CEs using the same methodology. If there are no pattern CEs in the rule at all, then an initial fact pattern is placed before the CE in question (unless facts have been disabled by configuring CLIPS in which case the initial object pattern is added before the CE). For example, the following rules


(defrule example-2

(test (> 80 (startup-value)))

⇒)


(defrule example-3

(test (> 80 (startup-value)))

(object (is-a MACHINE))

⇒)


(defrule example-4

(machine ?x)

(not (and (not (part ?x ?y))

(inventoried ?x)))

⇒)


would be changed as follows.


(defrule example-2

(initial-fact)

(test (> 80 (startup-value)))

⇒)


(defrule example-3

(object (is-a INITIAL-OBJECT) (name [initial-object]))

(test (> 80 (startup-value)))

(object (is-a MACHINE))

⇒)


(defrule example-4

(machine ?x)

(not (and (initial-fact)

(not (part ?x ?y))

(inventoried ?x)))

⇒)

5.4.9.3 Test CEs Following Not CEs

Test CEs that immediately follow a not CE are automatically moved by CLIPS behind the first pattern CE that precedes the not CE. For example, the following rule


(defrule example

(a ?x)

(not (b ?x))

(test (> ?x 5))

⇒)


would be changed as follows.


(defrule example

(a ?x)

(test (> ?x 5))

(not (b ?x))

⇒)

5.4.9.4 Or CEs Following Not CEs

If an or CE immediately follows a not CE, then the not/or CE combination is replaced with an and/not CE combination where each of the CEs contained in the original or CE is enclosed within a not CE and then all of the not CEs are enclosed within a single and CE. For example, the following rule


(defrule example

(a ?x)

(not (or (b ?x)

(c ?x)))

⇒)


would be changed as follows.


(defrule example

(a ?x)

(and (not (b ?x))

(not (c ?x)))

⇒)

5.4.9.5 Notes About Pattern Addition and Reordering

There are several points which should be noted about the addition and reordering of pattern CEs: 1) The entire LHS of a rule is considered to be within an implicit and CE; 2) The conversion of the forall and exists CEs to equivalent not and and CEs is performed before patterns are added to the LHS of a rule; 3) In general, it is not very useful to have a test CE as the first CE within an and CE; and 4) The output of commands such as the matches command display information for the CEs that are actually added to the LHS of a rule and, because of reordering and implicit additions, may not reflect the rule exactly as defined by the user.

5.4.10 Declaring Rule Properties

This feature allows the properties or characteristics of a rule to be defined. The char­acter­istics are declared on the LHS of a rule using the declare keyword. A rule may only have one declare statement and it must appear be­fore the first conditional element on the LHS (as shown in section 5.1).

Syntax

<declaration> ::= (declare <rule-property>+)


<rule-property> ::= (salience <integer-expression>) |

(auto-focus <boolean-symbol>)


<boolean-symbol> ::= TRUE | FALSE

5.4.10.1 The Salience Rule Property

The salience rule property allows the user to assign a priority to a rule. When multiple rules are in the agenda, the rule with the highest priority will fire first. The declared salience value should be an expression that evaluates to an an integer in the range  10000 to +10000. Salience expressions may freely reference global variables and other functions (however, you should avoid using functions with side effects). If unspecified, the salience value for a rule defaults to zero.

Example

(defrule test-1
(declare (salience 99))
(fire test-1)

(printout t “Rule test-1 firing.” crlf))


(defrule test-2
(declare (salience (+ ?*constraint-salience* 10)))

(fire test-2)

(printout t “Rule test-2 firing.” crlf))


Salience values can be evaluated at one of three times: when a rule is defined, when a rule is activated, and every cycle of execution (the latter two situations are referred to as dynamic salience). By default, salience values are only evaluated when a rule is defined. The set salience evaluation command can be used to change this behavior. Note that each salience evaluation method encompasses the previous method (i.e. if saliences are evaluated every cycle, then they are also evaluated when rules are activated or defined).

5.4.10.2 The Auto Focus Rule Property

The auto focus rule property allows an automatic focus command to be executed whenever a rule becomes activated. If the auto focus property for a rule is TRUE, then a focus command on the module in which the rule is defined is automatically executed whenever the rule is activated. If the auto focus property for a rule is FALSE, then no action is taken when the rule is activated. If unspecified, the auto focus value for a rule defaults to FALSE.

Example

(defrule VIOLATIONS::bad-age
(declare (auto-focus TRUE))
(person (name ?name) (age ?x&:(< ?x 0)))

(printout t ?name ” has a bad age value.“ crlf))

Section 6   Defglobal Construct

With the defglobal construct, global variables can be defined, set, and accessed within the CLIPS environment. Global variables can be accessed as part of the pattern matching process, but changing them does not invoke the pattern matching process. The bind function is used to set the value of global variables. Global variables are reset to their original value when the reset command is performed or when bind is called for the global with no values. This behavior can be changed using the set reset globals function. Global variables can be removed by using the clear command or the undefglobal command. If the globals item is being watched (see section 13.2), then an informational message will be displayed each time the value of a global variable is changed.

Syntax

(defglobal [<defmodule-name>] <global-assignment>*)


<global-assignment> ::= <global-variable> = <expression>


<global-variable> ::= ?*<symbol>*


There may be multiple defglobal constructs and any number of global variables may be defined in each defglobal statement. The optional <defmodule name> indicates the module in which the defglobals will be defined. If none is specified, the globals will be placed in the current module. If a variable was defined in a previous defglobal construct, its value will be replaced by the value found in the new defglobal construct. If an error is encountered when defining a defglobal construct, any global variable definitions that occurred before the error was encountered will still remain in effect.


Commands that operate on defglobals such as ppdefglobal and undefglobal expect the symbolic name of the global without the astericks (e.g. use the symbol max when you want to refer to the global variable ?*max*).


Global variables may be used anyplace that a local variable could be used (with two exceptions). Global variables may not be used as a parameter variable for a deffunction, defmethod, or message-handler. Global variables may not be used in the same way that a local variable is used on the LHS of a rule to bind a value. Therefore, the following rule is illegal


(defrule example

(fact ?*x*)

⇒)


The following rule, however, is legal.


(defrule example

(fact ?y&:(> ?y ?*x*))

⇒)


Note that this rule will not necessarily be updated when the value of ?*x* is changed. For example, if ?*x* is 4 and the fact (fact 3) is added, then the rule is not satisfied. If the value of ?*x* is now changed to 2, the rule will not be activated.

Example

(defglobal

?*x* = 3

?*y* = ?*x*

?*z* = (+ ?*x* ?*y*)

?*q* = (create$ a b c))


Section 7   Deffunction Construct

With the deffunction construct, new functions may be defined directly in CLIPS. Deffunctions are equivalent in use to other functions; see section 2.3.2 for more detail on calling functions in CLIPS. The only differences between user defined external functions and deffunctions are that deffunctions are written in CLIPS and executed by CLIPS interpretively and user defined external functions are written in an external language, such as C, and executed by CLIPS directly. Also, deffunctions allow the addition of new functions without having to recompile and relink CLIPS.


A deffunction is comprised of five elements: 1) a name, 2) an optional comment, 3) a list of zero or more required parameters, 4) an optional wildcard parameter to handle a variable number of arguments and 5) a sequence of actions, or expressions, which will be executed in order when the deffunction is called.

Syntax

(deffunction <name> [<comment>]

(<regular-parameter>* [<wildcard-parameter>])

<action>*)


<regular-parameter> ::= <single-field-variable>

<wildcard-parameter> ::= <multifield-variable>


A deffunction must have a unique name different from all other system functions and generic functions. In particular, a deffunction cannot be overloaded like a system function (see section 8 for more detail). A deffunction must be declared prior to being called from another deffunction, generic function method, object message handler, rule, or the top level. The only exception is a self recursive deffunction.


A deffunction may accept exactly or at least a specified number of arguments, depending on whether a wildcard parameter is used or not. The regular parameters specify the minimum number of arguments that must be passed to the deffunction. Each of these parameters may be referenced like a normal single field variable within the actions of the deffunction. If a wildcard parameter is present, the deffunction may be passed any number of arguments greater than or equal to the minimum. If no wildcard parameter is present, then the deffunction must be passed exactly the number of arguments specified by the regular parameters. All arguments to a deffunction that do not correspond to a regular parameter are grouped into a multifield value that can be referenced by the wildcard parameter. The standard CLIPS multifield functions, such as length and nth, can be applied to the wildcard parameter.

Example

CLIPS> (clear)

CLIPS>

(deffunction print-args (?a ?b $?c)

(printout t ?a ” “ ?b ” and “ (length ?c) ” extras: “ ?c

crlf))

CLIPS> (print-args 1 2)

1 2 and 0 extras: ()

CLIPS> (print-args a b c d)

a b and 2 extras: (c d)

CLIPS>


When a deffunction is called, its actions are executed in order. The return value of a deffunction is the evaluation of the last action. If a deffunction has no actions, its return value is the symbol FALSE. If an error occurs while the deffunction is executing, any actions not yet executed will be aborted, and the deffunction will return the symbol FALSE.


Deffunctions may be self and mutually recursive. Self recursion is accomplished simply by calling the deffunction from within its own actions.

Example

(deffunction factorial (?a)

(if (or (not (integerp ?a)) (< ?a 0)) then

(printout t “Factorial Error!” crlf)

else

(if (= ?a 0) then

1

else

(* ?a (factorial (- ?a 1))))))


Mutual recursion between two deffunctions requires a forward declaration of one of the deffunctions. A forward declaration is simply a declaration of the deffunction without any actions. In the following example, the deffunction foo is forward declared so that it may be called by the deffunction bar. Then the deffunction foo is redefined with actions that call the deffunction bar.

Example

(deffunction foo ())

(deffunction bar ()

(foo))

(deffunction foo ()

(bar))


Care should be taken with recursive deffunctions; too many levels of recursion can lead to an overflow of stack memory (especially on PC type machines).

Section 8   Generic Functions

With the defgeneric and defmethod constructs, new genericfunctions may be written directly in CLIPS. Generic functions are similar to deffunctions because they can be used to define new procedural code directly in CLIPS, and they can be called like any other function (see sections 2.3.2 and 7). However, generic functions are much more powerful because they can do different things depending on the types (or classes) and number of their arguments. For example, a “+” operator could be defined which performs concatenation for strings but still performs arithmetic addition for numbers. Generic functions are comprised of multiple components called methods, where each method handles different cases of arguments for the generic function. A generic function which has more than one method is said to be overloaded.


Generic functions can have system functions and user defined external functions as implicit methods. For example, an overloading of the “+” operator to handle strings consists of two methods: 1) an implicit one which is the system function handling numerical addition, and 2) an explicit (user defined) one handling string concatenation. Deffunctions, however, may not be methods of generic functions because they are subsumed by generic functions anyway. Deffunctions are only provided so that basic new functions can be added directly in CLIPS without the concerns of overloading. For example, a generic function which has only one method that restricts only the number of arguments is equivalent to a deffunction.


In most cases, generic function methods are not called directly (the function call specific method described in section 12.15.8 can be used to do so, however). CLIPS recognizes that a function call is generic and uses the generic function’s arguments to find and execute the appropriate method. This process is termed the generic dispatch.

8.1 Note on the Use of the Term Method

Most OOP systems support procedural behavior of objects either through message passing (e.g. Smalltalk) or by generic functions (e.g. CLOS). CLIPS supports both of these mechanisms, although generic functions are not strictly part of COOL. A generic function may examine the classes of its arguments but must still use messages within the bodies of its methods to manipulate any arguments which are instances of user defined classes. Section 9 gives more details on COOL. The fact that CLIPS supports both mechanisms leads to a confusion in terminology. In OOP systems which support message passing only, the term method is used to denote the different implementations of a message for different classes. In systems which support generic functions only, however, the term method is used to denote the different implementations of a generic function for different sets of argument restrictions. To avoid this confusion, the term message handleris used to take the place of method in the context of messages. Thus in CLIPS, message handlers denote the different implementations of a message for different classes, and methods denote the different implementations of a generic function for different sets of argument restrictions.

8.2 Performance Penalty of Generic Functions

A call to a generic function is computationally more expensive than a call to a system function, user defined external function or deffunction. This is because CLIPS must first examine the function arguments to determine which method is applicable. A performance penalty of 15% 20% is not unexpected. Thus, generic functions should not be used for routines for which time is critical, such as routines which are called within a while loop, if at all possible. Also, generic functions should always have at least two methods. Deffunctions or user defined external functions should be used when overloading is not required. A system or user defined external function which is not overloaded will, of course, execute as quickly as ever, since the generic dispatch is unnecessary.

8.3 Order Dependence of Generic Function Definitions

If a construct which uses a system or user defined external function is loaded before a generic function which uses that function as an implicit method, all calls to that function from that construct will bypass the generic dispatch. For example, if a generic function which overloads the “+” operator is defined after a rule which uses the “+” operator, that rule will always call the “+” system function directly. However, similar rules defined after the generic function will use the generic dispatch.

8.4 Defining a New Generic Function

A generic function is comprised of a header (similar to a forward declaration) and zero or more methods. A generic function header can either be explicitly declared by the user or implicitly declared by the definition of at least one method. A method is comprised of six elements: 1) a name (which identifies to which generic function the method belongs), 2) an optional index, 3) an optional comment , 4) a set of parameter restrictions, 5) an optional wildcard parameter restriction to handle a variable number of arguments and 6) a sequence of actions, or expressions, which will be executed in order when the method is called. The parameter restrictions are used by the generic dispatch to determine a method’s applicability to a set of arguments when the generic function is actually called. The defgeneric construct is used to specify the generic function header, and the defmethod construct is used for each of the generic function’s methods.


Syntax

(defgeneric <name> [<comment>])


(defmethod <name> [<index>] [<comment>]

(<parameter-restriction>* [<wildcard-parameter-restriction>])

<action>*)


<parameter-restriction> ::=

<single-field-variable> |

(<single-field-variable> <type>* [<query>])


<wildcard-parameter-restriction> ::=

<multifield-variable> |

(<multifield-variable> <type>* [<query>])


<type> ::= <class-name>

<query> ::= <global-variable> |

<function-call>


A generic function must be declared, either by a header or a method, prior to being called from another generic function method, deffunction, object message handler, rule, or the top level. The only exception is a self recursive generic function.

8.4.1 Generic Function Headers

A generic function is uniquely identified by name. In order to reference a generic function in other constructs before any of its methods are declared, an explicit header is necessary. Otherwise, the declaration of the first method implicitly creates a header. For example, two generic functions whose methods mutually call the other generic function (mutually recursive generic functions) would require explicit headers.

8.4.2 Method Indices

A method is uniquely identified by name and index, or by name and parameter restrictions. Each method for a generic function is assigned a unique integer index within the group of all methods for that generic function. Thus, if a new method is defined which has exactly the same name and parameter restrictions as another method, CLIPS will automatically replace the older method. However, any difference in parameter restrictions will cause the new method to be defined in addition to the older method. To replace an old method with one that has different parameter restrictions, the index of the old method can be explicitly specified in the new method definition. However, the parameter restrictions of the new method must not match that of another method with a different index. If an index is not specified, CLIPS assigns an index that has never been used by any method (past or current) of this generic function. The index assigned by CLIPS can be determined with the list defmethods command (see section 13.10.4).

8.4.3 Method Parameter Restrictions

Each parameter for a method can be defined to have arbitrarily complex restrictions or none at all. A parameter restriction is applied to a generic function argument at run time to determine if a particular method will accept the argument. A parameter can have two types of restrictions: type and query. A type restriction constrains the classes of arguments that will be accepted for a parameter. A query restriction is a user defined boolean test which must be satisfied for an argument to be acceptable. The complexity of parameter restrictions directly affects the speed of the generic dispatch.


A parameter that has no restrictions means that the method will accept any argument in that position. However, each method of a generic function must have parameter restrictions that make it distinguishable from all of the other methods so that the generic dispatch can tell which one to call at run time. If there are no applicable methods for a particular generic function call, CLIPS will generate an error (see section 8.5.4 for more detail).


A type restriction allows the user to specify a list of types (or classes), one of which must match (or be a superclass of) the class of the generic function argument. If COOL is not installed in the current CLIPS configuration, the only types (or classes) available are: OBJECT, PRIMITIVE, LEXEME, SYMBOL, STRING, NUMBER, INTEGER, FLOAT, MULTIFIELD, FACT ADDRESS and EXTERNAL ADDRESS. Section 9 describes each of these system classes. With COOL, INSTANCE, INSTANCE ADDRESS, INSTANCE NAME, USER, INITIAL OBJECT and any user defined classes are also available. Generic functions which use only the first group of types in their methods will work the same whether COOL is installed or not. The classes in a type restriction must be defined already, since they are used to predetermine the precedence between a generic function’s methods (see section 8.5.2 for more detail). Redundant classes are not allowed in restriction class lists. For example, the following method parameter’s type restriction is redundant since INTEGER is a subclass of NUMBER.

Example

(defmethod foo ((?a INTEGER NUMBER)))


If the type restriction (if any) is satisfied for an argument, then a query restriction (if any) will be applied. The query restriction must either be a global variable or a function call. CLIPS evaluates this expression, and if it evaluates to anything but the symbol FALSE, the restriction is considered satisfied. Since a query restriction is not always satisfied, queries should not have any side effects, for they will be evaluated for a method that may not end up being applicable to the generic function call. Since parameter restrictions are examined from left to right, queries which involve multiple parameters should be included with the rightmost parameter. This insures that all parameter type restrictions have already been satisfied. For example, the following method delays evaluation of the query restriction until the classes of both arguments have been verified.

Example

(defmethod foo ((?a INTEGER) (?b INTEGER (> ?a ?b))))


If the argument passes all these tests, it is deemed acceptable to a method. If all generic function arguments are accepted by a method’s restrictions, the method itself is deemed applicable to the set of arguments. When more than one method is applicable to a set of arguments, the generic dispatch must determine an ordering among them and execute the first one in that ordering. Method precedence is used for this purpose and will be discussed in section 8.5.2.

Example

In the following example, the first call to the generic function “+” executes the system operator “+”, an implicit method for numerical addition. The second call executes the explicit method for string concatenation, since there are two arguments and they are both strings. The third call generates an error because the explicit method for string concatenation only accepts two arguments and the implicit method for numerical addition does not accept strings at all.


CLIPS> (clear)

CLIPS>

(defmethod + ((?a STRING) (?b STRING))

(str-cat ?a ?b))

CLIPS> (+ 1 2)

3

CLIPS> (+ “foo” “bar”)

“foobar”

CLIPS> (+ “foo” “bar” “woz”)

[GENRCEXE1] No applicable methods for +.

FALSE

8.4.4 Method Wildcard Parameter

A method may accept exactly or at least a specified number of arguments, depending on whether a wildcard parameter is used or not. The regular parameters specify the minimum number of arguments that must be passed to the method. Each of these parameters may be referenced like a normal single field variable within the actions of the method. If a wildcard parameter is present, the method may be passed any number of arguments greater than or equal to the minimum. If no wildcard parameter is present, then the method must be passed exactly the number of arguments specified by the regular parameters. Method arguments which do not correspond to a regular parameter can be grouped into a multifield value that can be referenced by the wildcard parameter within the body of the method. The standard CLIPS multifield functions, such as length$ and expand$, can be applied to the wildcard parameter.


If multifield values are passed as extra arguments, they will all be merged into one multifield value referenced by the wildcard parameter. This is because CLIPS does not support nested multifield values.


Type and query restrictions can be applied to arguments grouped in the wildcard parameter similarly to regular parameters. Such restrictions apply to each individual field of the resulting multifield value (not the entire multifield). However, expressions involving the wildcard parameter variable may be used in the query. In addition, a special variable may be used in query restrictions on the wildcard parameter to refer to the individual arguments grouped into the wildcard: ?current argument. This variable is only in scope within the query and has no meaning in the body of the method. For example, to create a version of the ‘+’ operator which acts differently for sums of all even integers:

Example

CLIPS>

(defmethod +

(($?any INTEGER (evenp ?current-argument)))

(div (call-next-method) 2))

CLIPS> (+ 1 2)

3

CLIPS> (+ 4 6 4)

7

CLIPS>


It is important to emphasize that query and type restrictions on the wildcard parameter are applied to every argument grouped in the wildcard. Thus in the following example, the > and length$ functions are actually called three times, since there are three arguments:

Example

CLIPS> (defmethod foo (($?any (> (length$ ?any) 2))) yes)

CLIPS> (foo 1 red 3)

yes

CLIPS>


In addition, a query restriction will never be examined if there are no arguments in the wildcard parameter range. For example, the the previous methodwould be applicable to a call to the generic function with no arguments because the query restriction is never evaluated:

Example

CLIPS> (foo)

yes

CLIPS>


Typically query restrictions applied to the entire wildcard parameter are testing the cardinality (the number of arguments passed to the method). In cases like this where the type is irrelevant to the test, the query restriction can be attached to a regular parameter instead to improve performance (see section 8.5.1). Thus the previous method could be improved as follows:

Example

CLIPS> (clear)

CLIPS> (defmethod foo ((?arg (> (length$ ?any) 1)) $?any) yes)

CLIPS> (foo)

[GENRCEXE1] No applicable methods for foo.

FALSE

CLIPS>


This approach should not be used if the types of the arguments grouped by the wildcard must be verified prior to safely evaluating the query restriction.

8.5 Generic Dispatch

When a generic function is called, CLIPS selects the method for that generic function with highest precedence for which parameter restrictions are satisfied by the arguments. This method is executed, and its value is returned as the value of the generic function. This entire process is referred to as the generic dispatch. Below is a flow diagram summary:


| |

The solid arrows indicate automatic control transfer by the generic dispatch.
The dashed arrows indicate control transfer that can only be accomplished by the use or lack of the use of call next method or override next method |

8.5.1 Applicability of Methods Summary

An explicit (user defined) method is applicable to a generic function call if the following three conditions are met: 1) its name matches that of the generic function, 2) it accepts at least as many arguments as were passed to the generic function, and 3) every argument of the generic function satisfies the corresponding parameter restriction (if any) of the method.


Method restrictions are examined from left to right. As soon as one restriction is not satisfied, the method is abandoned, and the rest of the restrictions (if any) are not examined.


When a standard CLIPS system function is overloaded, CLIPS forms an implicit method definition corresponding to that system function. This implicit method is derived from the argument restriction string for the external DefineFunction2 call defining that function to CLIPS (see the Advanced Programming Guide). This string can be accessed with the function get function restrictions. The specification of this implicit method can be examined with the list defmethods or get method restrictions functions. The method that CLIPS will form for a system function can be derived by the user from the BNF given in this document. For example,


(+ <number> <number>+)


would yield the following method for the ‘+’ function:


(defmethod + ((?first NUMBER) (?second NUMBER) ($?rest NUMBER))

…)


The method definition is used to determine the applicability and precedence of the system function to the generic function call.


The following system functions cannot be overloaded, and CLIPS will generate an error if an attempt is made to do so.


| active duplicate instance | delayed do for all instances | message modify instance |

active initialize instance do for all instances modify
active make instance do for instance modify instance
active message duplicate instance duplicate next handlerp
active message modify instance duplicate instance next methodp
active modify instance expand$ object pattern match delay
any instancep find all instances override next handler
assert find instance override next method
bind if progn
break make instance progn$
call next handler initialize instance return
call next method loop for count switch
call specific method message duplicate instance while

8.5.2 Method Precedence

When two or more methods are applicable to a particular generic function call, CLIPS must pick the one with highest precedence for execution. Method precedence is determined when a method is defined; the list defmethods function can be used to examine the precedence of methods for a generic function (see section 13.10).


The precedence between two methods is determined by comparing their parameter restrictions. In general, the method with the most specific parameter restrictions has the highest precedence. For example, a method which demands an integer for a particular argument will have higher precedence than a method which only demands a number. The exact rules of precedence between two methods are given in order below; the result of the first rule which establishes precedence is taken.


1) ) The parameter restrictions of both methods are positionally compared from left to right. In other words, the first parameter restriction in the first method is matched against the first parameter restriction in the second method, and so on. The comparisons between these pairs of parameter restrictions from the two methods determine the overall precedence between the two methods. The result of the first pair of parameter restrictions which specifies precedence is taken. The following rules are applied in order to a parameter pair; the result of the first rule which establishes precedence is taken.


1a) A regular parameter has precedence over a wildcard parameter.

1b) The most specific type restriction on a particular parameter has priority. A class is more specific than any of its superclasses.

1c) A parameter with a query restriction has priority over one that does not.


2) The method with the greater number of regular parameters has precedence.


3) A method without a wildcard parameter has precedence over one that does


4) A method defined before another one has priority.


If there are multiple classes on a single restriction, determining specificity is slightly more complicated. Since all precedence determination is done when the new method is defined, and the actual class of the generic function argument will not be known until run time, arbitrary (but deterministic) rules are needed for determining the precedence between two class lists. The two class lists are examined by pairs from left to right, e.g. the pair of first classes from both lists, the pair of second classes from both lists and so on. The first pair containing a class and its superclass specify precedence. The class list containing the subclass has priority. If no class pairs specify precedence, then the shorter class list has priority. Otherwise, the class lists do not specify precedence between the parameter restrictions.

Example 1

; The system operator '+' is an implicit method ; #1

; Its definition provided by the system is:

; (defmethod + ((?a NUMBER) (?b NUMBER) ($?rest NUMBER)))


(defmethod + ((?a NUMBER) (?b INTEGER))) ; #2

(defmethod + ((?a INTEGER) (?b INTEGER))) ; #3

(defmethod + ((?a INTEGER) (?b NUMBER))) ; #4

(defmethod + ((?a NUMBER) (?b NUMBER)

($?rest PRIMITIVE))) ; #5

(defmethod + ((?a NUMBER)

(?b INTEGER (> ?b 2)))) ; #6

(defmethod + ((?a INTEGER (> ?a 2))

(?b INTEGER (> ?b 3)))) ; #7

(defmethod + ((?a INTEGER (> ?a 2))

(?b NUMBER))) ; #8


The precedence would be: #7,#8,#3,#4,#6,#2,#1,#5. The methods can be immediately partitioned into three groups of decreasing precedence according to their restrictions on the first parameter: A) methods which have a query restriction and a type restriction of INTEGER (#7,#8), B) methods which have a type restriction of INTEGER (#3,#4), and C) methods which have a type restriction of NUMBER (#1,#2,#5,#6). Group A has precedence over group B because parameters with query restrictions have priority over those that do not. Group B has precedence over group C because INTEGER is a subclass of NUMBER. Thus, the ordering so far is: (#7,#8),(#3,#4),(#1,#2,#5,#6). Ordering between the methods in a particular set of parentheses is not yet established.


The next step in determining precedence between these methods considers their restrictions on the second parameter. #7 has priority over #8 because INTEGER is a subclass of NUMBER. #3 has priority over #4 because INTEGER is a subclass of NUMBER. #6 and #2 have priority over #1 and #5 because INTEGER is a subclass of NUMBER. #6 has priority over #2 because it has a query restriction and #2 does not. Thus the ordering is now: #7,#8,#3,#4,#6,#2,(#1,#5).


The restriction on the wildcard argument yields that #1 (the system function implicit method) has priority over #5 since NUMBER is a sublclass of PRIMITIVE. This gives the final ordering: #7,#8,#3,#4,#6,#2,#1,#5.

Example 2

(defmethod foo ((?a NUMBER STRING))) ; #1

(defmethod foo ((?a INTEGER LEXEME))) ; #2


The precedence would be #2,#1. Although STRING is a subclass of LEXEME, the ordering is still #2,#1 because INTEGER is a subclass of NUMBER, and NUMBER/INTEGER is the leftmost pair in the class lists.

Example 3

(defmethod foo ((?a MULTIFIELD STRING))) ; #1

(defmethod foo ((?a LEXEME))) ; #2


The precedence would be #2,#1 because the classes of the first pair in the type restriction (MULTIFIELD/LEXEME) are unrelated and #2 has fewer classes in its class list.

Example 4

(defmethod foo ((?a INTEGER LEXEME))) ; #1

(defmethod foo ((?a STRING NUMBER))) ; #2


Both pairs of classes (INTEGER/STRING and LEXEME/NUMBER) are unrelated, and the class lists are of equal length. Thus, the precedence is taken from the order of definition: #1,#2.

8.5.3 Shadowed Methods

If one method must be called by another method in order to be executed, the first function or method is a said to be shadowed by the second method. Normally, only one method or system function will be applicable to a particular generic function call. If there is more than one applicable method, the generic dispatch will only execute the one with highest precedence. Letting the generic dispatch automatically handle the methods in this manner is called the declarative technique, for the declarations of the method restrictions dictate which method gets executed in specific circumstances. However, the functions call next method and override next method (see section 12.15.6 and 12.15.7) may also be used which allow a method to execute the method that it is shadowing. This is called the imperative technique, since the method execution itself plays a role in the generic dispatch. This is not recommended unless it is absolutely necessary. In most circumstances, only one piece of code should need to be executed for a particular set of arguments. Another imperative technique is to use the function call specific method to override method precedence (see section 12.15.8)

8.5.4 Method Execution Errors

If an error occurs while any method for a generic function call is executing, any actions in the current method not yet executed will be aborted, any methods not yet called will be aborted, and the generic function will return the symbol FALSE. The lack of any applicable methods for a set of generic function arguments is considered a method execution error.

8.5.5 Generic Function Return Value

The return value of a generic function is the return value of the applicable method with the highest precedence. Each applicable method that is executed can choose to ignore or capture the return value of any method that it is shadowing.


The return value of a particular method is the last action evaluated by that method.

Section 9   CLIPS Object Oriented Language (COOL)

This section provides the comprehensive details of the CLIPS Object Oriented Language (COOL). Sections 2.3.1, 2.4.2 and 2.5.2.3 explain object references and structure. Section 2.6 gives a high level overview of COOL. This section assumes a complete understanding of the material given in the listed sections.

9.1 Background

COOL is a hybrid of features from many different OOP systems as well as new ideas. For example, object encapsulation concepts are similar to those in Smalltalk, and the Common Lisp Object System (CLOS) provides the basis for multiple inheritance rules. A mixture of ideas from Smalltalk, CLOS and other systems form the foundation of messages. Section 8.1 explains an important contrast between the terms method and message handler in CLIPS.

9.2 Predefined System Classes

COOL provides seventeen system classes: OBJECT, USER, INITIAL OBJECT, PRIMITIVE, NUMBER, INTEGER, FLOAT, INSTANCE, INSTANCE NAME, INSTANCE ADDRESS, ADDRESS, FACT ADDRESS, EXTERNAL ADDRESS, MULTIFIELD, LEXEME, SYMBOL and STRING. The user may not delete or modify any of these classes. The diagram illustrates the inheritance relationships between these classes.


All of these system classes except INITIAL OBJECT are abstract classes, which means that their only use is for inheritance (direct instances of this class are illegal). None of these classes have slots, and, except for the class USER, none of them have message handlers. However, the user may explicitly attach message handlers to all of the system classes except for INSTANCE, INSTANCE ADDRESS and INSTANCE NAME. The OBJECT class is a superclass of all other classes, including user defined classes. All user defined classes should (but are not required to) inherit directly or indirectly from the class USER, since this class has all of the standard system message handlers, such as initialization and deletion, attached to it. Section 9.4 describes these system message handlers.


The PRIMITIVE system class and all of its subclasses are provided mostly for use in generic function method restrictions, but message handlers and new subclasses may be attached if desired. However, the three primitive system classes INSTANCE, INSTANCE ADDRESS and INSTANCE NAME are provided strictly for use in methods (particularly in forming implicit methods for overloaded system functions - see section 8.5.1) and as such cannot have subclasses or message handlers attached to them.


The INITIAL OBJECT class is provided for use by the default definstances initial object in creating the default instance [initial object] during the reset command. This system class is concrete and reactive to pattern matching on the LHS of rules but is in other respects exactly like the system class USER. The instance [initial object] is for use by the initial object pattern (see section 5.4.9).

9.3 Defclass Construct

A defclass is a construct for specifying the properties (slots) and behavior (message handlers) of a class of objects. A defclass consists of five elements: 1) a name, 2) a list of superclasses from which the new class inherits slots and message handlers, 3) a specifier saying whether or not the creation of direct instances of the new class is allowed, 4) a specifier saying whether or not instances of this class can match object patterns on the LHS of rules and 5) a list of slots specific to the new class. All user defined classes must inherit from at least one class, and to this end COOL provides predefined system classes for use as a base in the derivation of new classes.


Any slots explicitly given in the defclass override those gotten from inheritance. COOL applies rules to the list of superclasses to generate a class precedence list (see section 9.3.1) for the new class. Facets (see section 9.3.3) further describe slots. Some examples of facets include: default value, cardinality, and types of access allowed.

Syntax

Defaults are outlined.


(defclass <name> [<comment>]

(is-a <superclass-name>+)

[<role>]

[<pattern-match-role>]

<slot>*

<handler-documentation>*)


<role> ::= (role concrete | abstract)


<pattern-match-role>

::= (pattern-match reactive | non-reactive)


<slot> ::= (slot <name> <facet>*) |

(single-slot <name> <facet>*) |

(multislot <name> <facet>*)


<facet> ::= <default-facet> | <storage-facet> |

<access-facet> | <propagation-facet> |

<source-facet> | <pattern-match-facet> |

<visibility-facet> | <create-accessor-facet>

<override-message-facet> | <constraint-attributes>

<default-facet> ::=

(default ?DERIVE | ?NONE | <expression>*) |

(default-dynamic <expression>*)


<storage-facet> ::= (storage local | shared)


<access-facet>

::= (access read-write | read-only | initialize-only)


<propagation-facet> ::= (propagation inherit | no-inherit)


<source-facet> ::= (source exclusive | composite)


<pattern-match-facet>

::= (pattern-match reactive | non-reactive)


<visibility-facet> ::= (visibility private | public)


<create-accessor-facet>

::= (create-accessor ?NONE | read | write | read-write)


<override-message-facet>

::= (override-message ?DEFAULT | <message-name>)

<handler-documentation>

::= (message-handler <name> [<handler-type>])


<handler-type> ::= primary | around | before | after


Redefining an existing class deletes the current subclasses and all associated message handlers. An error will occur if instances of the class or any of its subclasses exist.

9.3.1 Multiple Inheritance

If one class inherits from another class, the first class is a subclass of the second class, and the second class is a superclass of the first class. Every user defined class must have at least one direct superclass, i.e. at least one class must appear in the is a portion of the defclass. Multiple inheritance occurs when a class has more than one direct superclass. COOL examines the direct superclass list for a new class to establish a linear ordering called theclass precedence list. The new class inherits slots and message handlers from each of the classes in the class precedence list. The word precedence implies that slots and message handlers of a class in the list override conflicting definitions of another class found later in the list. A class that comes before another class in the list is said to be more specific. All class precedence lists will terminate in the system class OBJECT, and most (if not all) class precedence lists for user defined classes will terminate in the system classes USER and OBJECT. The class precedence list can be listed using the describe class function (see section 13.11.1.4).

9.3.1.1 Multiple Inheritance Rules

COOL uses the inheritance hierarchy of the direct superclasses to determine the class precedence list for a new class. COOL recursively applies the following two rules to the direct superclasses:


1) A class has higher precedence than any of its superclasses.

2) A class specifies the precedence between its direct superclasses.


If more than one class precedence list would satisfy these rules, COOL chooses the one most similar to a strict preorder depth first traversal. This heuristic attempts to preserve “family trees” to the greatest extent possible. For example, if a child inherited genetic traits from a mother and father, and the mother and father each inherited traits from their parents, the child’s class precedence list would be: child mother maternal grandmother maternal grandfather father paternal grandmother paternal grandfather. There are other orderings which would satisfy the rules (such as child mother father paternal grandfather maternal grandmother paternal grandmother maternal grandfather), but COOL chooses the one which keeps the family trees together as much as possible.

Example 1

(defclass A (is-a USER))


Class A directly inherits information from the class USER. The class precedence list for A is: A USER OBJECT.

Example 2

(defclass B (is-a USER))


Class B directly inherits information from the class USER. The class precedence list for B is: B USER OBJECT.

Example 3

(defclass C (is-a A B))


Class C directly inherits information from the classes A and B. The class precedence list for C is: C A B USER OBJECT.

Example 4

(defclass D (is-a B A))


Class D directly inherits information from the classes B and A. The class precedence list for D is: D B A USER OBJECT.

Example 5

(defclass E (is-a A C))


By rule #2, A must precede C. However, C is a subclass of A and cannot succeed A in a precedence list without violating rule #1. Thus, this is an error.

Example 6

(defclass E (is-a C A))


Specifying that E inherits from A is extraneous, since C inherits from A. However, this definition does not violate any rules and is acceptable. The class precedence list for E is: E C A B USER OBJECT.

Example 7

(defclass F (is-a C B))


Specifying that F inherits from B is extraneous, since C inherits from B. The class precedence list for F is: F C A B USER OBJECT. The superclass list says B must follow C in F’s class precedence list but not that B must immediately follow C.

Example 8

(defclass G (is-a C D))


This is an error, for it violates rule #2. The class precedence of C says that A should precede B, but the class precedence list of D says the opposite.

Example 9

(defclass H (is-a A))

(defclass I (is-a B))

(defclass J (is-a H I A B))


The respective class precedence lists of H and I are: H A USER OBJECT and I B USER OBJECT. If J did not have A and B as direct superclasses, J could have one of three possible class precedence lists: J H A I B USER OBJECT, J H I A B USER OBJECT or J H I B A USER OBJECT. COOL would normally pick the first list since it preserves the family trees (H A and I B) to the greatest extent possible. However, since J inherits directly from A and B, rule #2 dictates that the class precedence list must be J H I A B USER OBJECT.

9.3.2 Class Specifiers

9.3.2.1 Abstract and Concrete Classes

An abstract class is intended for inheritance only, and no direct instances of this class can be created. A concrete class can have direct instances. Using the abstract role specifier in a defclass will cause COOL to generate an error if make instance is ever called for this class. If the abstract or concrete descriptor for a class is not specified, it is determined by inheritance. For the purpose of role inheritance, system defined classes behave as concrete classes. Thus a class which inherits from USER will be concrete if no role is specified.

9.3.2.2 Reactive and Non Reactive Classes

Objects of a reactive class can match object patterns in a rule. Objects of a non reactive class cannot match object patterns in a rule and are not considered when the list of applicable classes are determined for an object pattern. An abstract class cannot be reactive. If the reactive or non reactive descriptor for a class is not specified, it is determined by inheritance. For the purpose of pattern-match inheritance, system defined classes behave as reactive classes unless the inheriting class is abstract.

9.3.3 Slots

Slots are placeholders for values associated with instances of a user defined class. Each instance has a copy of the set of slots specified by the immediate class as well as any obtained from inheritance. Only available memory limits the number of slots. The name of a slot may be any symbol with the exception of the keywords is a and name which are reserved for use in object patterns.


To determine the set of slots for an instance, the class precedence list for the instance’s class is examined in order from most specific to most general (left to right). A class is more specific than its superclasses. Slots specified in any of the classes in the class precedence list are given to the instance, with the exception of no inherit slots (see section 9.3.3.5). If a slot is inherited from more than one class, the definition given by the more specific class takes precedence, with the exception of composite slots (see section 9.3.3.6).

Example

(defclass A (is-a USER)

(slot fooA)

(slot barA))


(defclass B (is-a A)

(slot fooB)

(slot barB))


The class precedence list of A is: A USER OBJECT. Instances of A will have two slots: fooA and barA. The class precedence list of B is: B A USER OBJECT. Instances of B will have four slots: fooB, barB, fooA and barA.


Just as slots make up classes, facets make up slots. Facets describe various features of a slot that hold true for all objects which have the slot: default value, storage, access, inheritance propagation, source of other facets, pattern matching reactivity, visibility to subclass message handlers, the automatic creation of message handlers to access the slot, the name of the message to send to set the slot and constraint information. Each object can still have its own value for a slot, with the exception of shared slots (see section 9.3.3.3).

9.3.3.1 Slot Field Type

A slot can hold either a single field or multifield value. By default, a slot is single field. The keyword multislot specifies that a slot can hold a multifield value comprised of zero or more fields, and the keywords slot or single slot specify that the slot can hold one value. Multifield slot values are stored as multifield values and can be manipulated with the standard multifield functions, such as nth$ and length$, once they are retrieved via messages. COOL also provides functions for setting multifield slots, such as slot insert$(see section 12.16.4.12.2). Single field slots are stored as a CLIPS primitive type, such as integer or string.

Example

CLIPS> (clear)

CLIPS>

(defclass A (is-a USER)

(role concrete)

(multislot foo (create-accessor read)

(default abc def ghi)))

CLIPS> (make-instance a of A)

[a]

CLIPS> (nth$ 2 (send [a] get-foo))

def

CLIPS>

9.3.3.2 Default Value Facet

The default and default dynamic facets can be used to specify an initial value given to a slot when an instance of the class is created or initialized. By default, a slot will have a default value which is derived from the slot’s constraint facets (see sections 9.3.3.11 and 11.5). Default values are directly assigned to slots without the use of messages, unlike slot overrides in a make instance call (see section 9.6.1).


The default facet is a static default: the specified expression is evaluated once when the class is defined, and the result is stored with the class. This result is assigned to the appropriate slot when a new instance is created. If the keyword ?DERIVE is used for the default value, then a default value is derived from the constraints for the slot (see section 11.5 for more details). By default, the default attribute for a slot is (default ?DERIVE). If the keyword ?NONE is used for the default value, then the slot is not assigned a default value. Using this keyword causes make instance to require a slot override for that slot when an instance is created. Note that in CLIPS 6.0, a slot now has a default even if one is not explicitly specified (unlike CLIPS 5.1). This could cause different behavior for CLIPS 5.1 programs using the initialize instance function. The ?NONE keyword can be used to recover the original behavior for classes.


The default dynamic facet is a dynamic default: the specified expression is evaluated every time an instance is created, and the result is assigned to the appropriate slot.

Example

CLIPS> (clear)

CLIPS> (setgen 1)

1

CLIPS>

(defclass A (is-a USER)

(role concrete)

(slot foo (default-dynamic (gensym))

(create-accessor read)))

CLIPS> (make-instance a1 of A)

[a1]

CLIPS> (make-instance a2 of A)

[a2]

CLIPS> (send [a1] get-foo)

gen1

CLIPS> (send [a2] get-foo)

gen2

CLIPS>

9.3.3.3 Storage Facet

The actual value of an instance’s copy of a slot can either be stored with the instance or with the class. The local facet specifies that the value be stored with the instance, and this is the default. The shared facet specifies that the value be stored with the class. If the slot value is locally stored, then each instance can have a separate value for the slot. However, if the slot value is stored with the class, all instances will have the same value for the slot. Anytime the value is changed for a shared slot, it will be changed for all instances with that slot.


A shared slot will always pick up a dynamic default value from a defclass when an instance is created or initialized, but the shared slot will ignore a static default value unless it does not currently have a value. Any changes to a shared slot will cause pattern matching for rules to be updated for all reactive instances containing that slot.

Example

CLIPS> (clear)

CLIPS>

(defclass A (is-a USER)

(role concrete)

(slot foo (create-accessor write)

(storage shared)

(default 1))

(slot bar (create-accessor write)

(storage shared)

(default-dynamic 2))

(slot woz (create-accessor write)

(storage local)))

CLIPS> (make-instance a of A)

[a]

CLIPS> (send [a] print)

[a] of A

(foo 1)

(bar 2)

(woz nil)

CLIPS> (send [a] put-foo 56)

56

CLIPS> (send [a] put-bar 104)

104

CLIPS> (make-instance b of A)

[b]

CLIPS> (send [b] print)

[b] of A

(foo 56)

(bar 2)

(woz nil)

CLIPS> (send [b] put-foo 34)

34

CLIPS> (send [b] put-woz 68)

68

CLIPS> (send [a] print)

[a] of A

(foo 34)

(bar 2)

(woz nil)

CLIPS> (send [b] print)

[b] of A

(foo 34)

(bar 2)

(woz 68)

CLIPS>

9.3.3.4 Access Facet

There are three types of access facets which can be specified for a slot: read write, read only, and initialize only. The read write facet is the default and says that a slot can be both written and read. The read only facet says the slot can only be read; the only way to set this slot is with default facets in the class definition. The initialize only facet is like read only except that the slot can also be set by slot overrides in a make instance call(see section 9.6.1) and init message handlers (see section 9.4). These privileges apply to indirect access via messages as well as direct access within message handler bodies (see section 9.4). Note: a read only slot that has a static default value will implicitly have the shared storage facet.

Example

CLIPS> (clear)

CLIPS>

(defclass A (is-a USER)

(role concrete)

(slot foo (create-accessor write)

(access read-write))

(slot bar (access read-only)

(default abc))

(slot woz (create-accessor write)

(access initialize-only)))

CLIPS>

(defmessage-handler A put-bar (?value)

(dynamic-put (sym-cat bar) ?value))

CLIPS> (make-instance a of A (bar 34))

[MSGFUN3] bar slot in [a] of A: write access denied.

[PRCCODE4] Execution halted during the actions of message-handler put-bar primary in class A

FALSE

CLIPS> (make-instance a of A (foo 34) (woz 65))

[a]

CLIPS> (send [a] put-bar 1)

[MSGFUN3] bar slot in [a] of A: write access denied.

[PRCCODE4] Execution halted during the actions of message-handler put-bar primary in class A

FALSE

CLIPS> (send [a] put-woz 1)

[MSGFUN3] woz slot in [a] of A: write access denied.

[PRCCODE4] Execution halted during the actions of message-handler put-bar primary in class A

FALSE

CLIPS> (send [a] print)

[a] of A

(foo 34)

(bar abc)

(woz 65)

CLIPS>

9.3.3.5 Inheritance Propagation Facet

An inherit facet says that a slot in a class can be given to instances of other classes that inherit from the first class. This is the default. The no inherit facet says that only direct instances of this class will get the slot.

Example

CLIPS> (clear)

CLIPS>

(defclass A (is-a USER)

(role concrete)

(slot foo (propagation inherit))

(slot bar (propagation no-inherit)))

CLIPS> (defclass B (is-a A))

CLIPS> (make-instance a of A)

[a]

CLIPS> (make-instance b of B)

[b]

CLIPS> (send [a] print)

[a] of A

(foo nil)

(bar nil)

CLIPS> (send [b] print)

[b] of B

(foo nil)

CLIPS>

9.3.3.6 Source Facet

When obtaining slots from the class precedence list during instance creation, the default behavior is to take the facets from the most specific class which gives the slot and give default values to any unspecified facets. This is the behavior specified by the exclusive facet. The composite facet causes facets which are not explicitly specified by the most specific class to be taken from the next most specific class. Thus, in an overlay fashion, the facets of an instance’s slot can be specified by more than one class. Note that even though facets may be taken from superclasses, the slot is still considered to reside in the new class for purposes of visibility (see section 9.3.3.8). One good example of a use of this feature is to pick up a slot definition and change only its default value for a new derived class.

Example

CLIPS> (clear)

CLIPS>

(defclass A (is-a USER)

(multislot foo (access read-only)

(default a b c)))

CLIPS>

(defclass B (is-a A)

(slot foo (source composite) ; multiple and read-only

; from class A

(default d e f)))

CLIPS> (describe-class B)

===============================================================

***************************************************************

Abstract: direct instances of this class cannot be created.


Direct Superclasses: A

Inheritance Precedence: B A USER OBJECT

Direct Subclasses:

---------------------------------------------------------------

SLOTS : FLD DEF PRP ACC STO MCH SRC VIS CRT OVRD-MSG SOURCE(S)

foo : MLT STC INH R LCL RCT CMP PRV NIL NIL A B


Constraint information for slots:


SLOTS : SYM STR INN INA EXA FTA INT FLT

foo : + + + + + + + + RNG:[-oo..+oo] CRD:[0..+oo]

---------------------------------------------------------------

Recognized message-handlers:

init primary in class USER

delete primary in class USER

create primary in class USER

print primary in class USER

direct-modify primary in class USER

message-modify primary in class USER

direct-duplicate primary in class USER

message-duplicate primary in class USER

***************************************************************

===============================================================

CLIPS>

9.3.3.7 Pattern Match Reactivity Facet

Normally, any change to a slot of an instance will be considered as a change to the instance for purposes of pattern matching. However, it is possible to indicate that changes to a slot of an instance should not cause pattern matching. The reactive facet specifies that changes to a slot trigger pattern matching, and this is the default. The non reactive facet specifies that changes to a slot do not affect pattern matching.

Example

CLIPS> (clear)

CLIPS>

(defclass A (is-a USER)

(role concrete)

(pattern-match reactive)

(slot foo (create-accessor write)

(pattern-match non-reactive)))

CLIPS>

(defclass B (is-a USER)

(role concrete)

(pattern-match reactive)

(slot foo (create-accessor write)

(pattern-match reactive)))

CLIPS>

(defrule Create

?ins←(object (is-a A | B))

(printout t “Create ” (instance-name ?ins) crlf))

CLIPS>

(defrule Foo-Access

?ins←(object (is-a A | B) (foo ?))

(printout t “Foo-Access ” (instance-name ?ins) crlf))

CLIPS> (make-instance a of A)

[a]

CLIPS> (make-instance b of B)

[b]

CLIPS> (run)

Create [b]

Foo-Access [b]

Create [a]

CLIPS> (send [a] put-foo 1)

1

CLIPS> (send [b] put-foo 1)

1

CLIPS> (run)

Foo-Access [b]

CLIPS>

9.3.3.8 Visibility Facet

Normally, only message handlers attached to the class in which a slot is defined may directly access the slot. However, it is possible to allow message handlers attached to superclasses or subclasses which inherit the slot to directly access the slot as well. Declaring the visibility facet to be private specifies that only the message handlers of the defining class may directly access the slot, and this is the default. Declaring the visibility facet to be public specifies that the message handlers and subclasses which inherit the slot and superclasses may also directly access the slot.

Example

CLIPS> (clear)

CLIPS>

(defclass A (is-a USER)

(slot foo (visibility private)))

CLIPS>

(defclass B (is-a A)

(role concrete))

CLIPS>

(defmessage-handler B get-foo ()

?self:foo)

[MSGFUN6] Private slot foo of class A cannot be accessed directly by handlers attached to class B


[PRCCODE3] Undefined variable self:foo referenced in message-handler.


ERROR:

(defmessage-handler MAIN::B get-foo

()

?self:foo

)

CLIPS>

9.3.3.9 Create Accessor Facet

The create accessor facet instructs CLIPS to automatically create explicit message handlers for reading and/or writing a slot. By default, implicit slot accessor message handlers are created for every slot. While these message handlers are real message handlers and can be manipulated as such, they have no pretty print form and cannot be directly modified by the user.


If the value ?NONE is specified for the facet, no message-handlers are created.


If the value read is specified for the facet, CLIPS creates the following message handler:


(defmessage-handler <class> get-<slot-name> primary ()

?self:<slot-name>)


If the value write is specified for the facet, CLIPS creates the following message handler for single field slots:


(defmessage-handler <class> put-<slot-name> primary (?value)

(bind ?self:<slot-name> ?value)


or the following message handler for multifield slots:


(defmessage-handler <class> put-<slot-name> primary ($?value)

(bind ?self:<slot-name> ?value)


If the value read write is specified for the facet, both the get  and one of the put  message handlers are created.


If accessors are required that do not use static slot references (see sections 9.4.2, 9.6.3 and 9.6.4), then user must define them explicitly with the defmessage handler construct.


The access facet affects the default value for the the create accessor facet. If the access facet is read-write, then the default value for the create-accessor facet is read-write. If the access facet is read-only, then the default value is read. If the access facet is initialize only, then the default is ?NONE.

Example

CLIPS> (clear)

CLIPS>

(defclass A (is-a USER)

(role concrete)

(slot foo (create-accessor write))

(slot bar (create-accessor read))

CLIPS> (make-instance a of A (foo 36))

[a]

CLIPS> (make-instance b of A (bar 45))

[MSGFUN1] No applicable primary message-handlers found for put-bar.

FALSE

CLIPS>

9.3.3.10 Override Message Facet

There are several COOL support functions which set slots via use of message passing, e.g., make instance, initialize instance, message modify instance and message duplicate instance. By default, all these functions attempt to set a slot with the message called put <slot name>. However, if the user has elected not to use standard slot accessors and wishes these functions to be able to perform slot overrides, then the override message facet can be used to indicate what message to send instead.

Example

CLIPS> (clear)

CLIPS>

(defclass A (is-a USER)

(role concrete)

(slot special (override-message special-put)))

CLIPS>

(defmessage-handler A special-put primary (?value)

(bind ?self:special ?value))

CLIPS> (watch messages)

CLIPS> (make-instance a of A (special 65))

MSG » create ED:1 (<Instance-a>)

MSG « create ED:1 (<Instance-a>)

MSG » special-put ED:1 (<Instance-a> 65)

MSG « special-put ED:1 (<Instance-a> 65)

MSG » init ED:1 (<Instance-a>)

MSG « init ED:1 (<Instance-a>)

[a]

CLIPS> (unwatch messages)

CLIPS>

9.3.3.11 Constraint Facets

The syntax and functionality of single and multifield constraint facets (attributes) are described in detail in Section 11. Static and dynamic constraint checking for classes and their instances is supported. Static checking is performed when constructs or commands which specify slot information are being parsed. Object patterns used on the LHS of a rule are also checked to determine if constraint conflicts exist among variables used in more that one slot. Errors for inappropriate values are immediately signaled. Static checking is enabled by default. This behavior can be changed using the set static constraint checking function. Dynamic checking is also supported. If dynamic checking is enabled, then new instances have their values checked whenever they are set (e.g. initialization, slot overrides, and put  access). This dynamic checking is disabled by default. This behavior can be changed using the set dynamic constraint checking function. If an violation occurs when dynamic checking is being performed, then execution will be halted.


Regardless of whether static or dynamic checking is enabled, multifield values can never be stored in single field slots. Single field values are converted to a multifield value of length one when storing in a multifield slot. In addition, the evaluation of a function which has no return value is always illegal as a slot value.

Example

CLIPS> (clear)

CLIPS>

(defclass A (is-a USER)

(role concrete)

(multislot foo (create-accessor write)

(type SYMBOL)

(cardinality 2 3)))

CLIPS> (make-instance a of A (foo 45))

[a]

CLIPS> (set-dynamic-constraint-checking TRUE)

FALSE

CLIPS> (make-instance a of A (foo red 5.0))

[CSTRNCHK1] (red 5.0) for slot foo of instance [a] found in put-foo primary in class A does not match the allowed types.

[PRCCODE4] Execution halted during the actions of message-handler put-foo primary in class A

FALSE

CLIPS> (make-instance a of A (foo red))

[CSTRNCHK1] (red) for slot foo of instance [a] found in put-foo primary in class A does not satisfy the cardinality restrictions.

[PRCCODE4] Execution halted during the actions of message-handler put-foo primary in class A

FALSE

CLIPS>

9.3.4 Message handler Documentation

COOL allows the user to forward declare the message handlers for a class within the defclass statement. These declarations are for documentation only and are ignored by CLIPS. The defmessage handler construct must be used to actually add message handlers to a class. Message handlers can later be added which are not documented in the defclass.

Example

CLIPS> (clear)

CLIPS>

(defclass rectangle (is-a USER)

(slot side-a (default 1))

(slot side-b (default 1))

(message-handler find-area))

CLIPS>

(defmessage-handler rectangle find-area ()

(* ?self:side-a ?self:side-b))

CLIPS>

(defmessage-handler rectangle print-area ()

(printout t (send ?self find-area) crlf))

CLIPS>

9.4 Defmessage handler Construct

Objects are manipulated by sending them messages via the function send. The result of a message is a useful return value or side effect. A defmessage handler is a construct for specifying the behavior of a class of objects in response to a particular message. The implementation of a message is made up of pieces of procedural code called message handlers (or handlers for short). Each class in the class precedence list of an object’s class can have handlers for a message. In this way, the object’s class and all its superclasses share the labor of handling the message. Each class’s handlers handle the part of the message which is appropriate to that class. Within a class, the handlers for a particular message can be further subdivided into four types or categories: primary, before, after and around. The intended purposes of each type are summarized in the chart below:


* Type Role for the Class primary Performs the majority of the work for the message before Does auxiliary work for a message before the primary handler executes after Does auxiliary work for a message after the primary handler executes around Sets up an environment for the execution of the rest of the handlers


Before and after handlers are for side effects only; their return values are always ignored. Before handlers execute before the primaryones, and after message handlers execute after the primary ones. The return value of a message is generally given by the primary message handlers, but around handlers can also return a value. Around message handlers allow the user to wrap code around the rest of the handlers. They begin execution before the other handlers and pick up again after all the other message handlers have finished.


A primary handler provides the part of the message implementation which is most specific to an object, and thus the primary handler attached to the class closest to the immediate class of the object overrides other primary handlers. Before and after handlers provide the ability to pick up behavior from classes that are more general than the immediate class of the object, thus the message implementation uses all handlers of this type from all the classes of an object. When only the roles of the handlers specify which handlers get executed and in what order, the message is said to be declaratively implemented. However, some message implementations may not fit this model well. For example, the results of more than one primary handler may be needed. In cases like this, the handlers themselves must take part in deciding which handlers get executed and in what order. This is called the imperative technique. Around handlers provide imperative control over all other types of handlers except more specific around handlers. Around handlers can change the environment in which other handlers execute and modify the return value for the entire message. A message implementation should use the declarative technique if at all possible because this allows the handlers to be more independent and modular.


A defmessage handler is comprised of seven elements: 1) a class name to which to attach the handler (the class must have been previously defined), 2) a message name to which the handler will respond, 3) an optional type (the default is primary), 4) an optional comment, 5) a list of parameters that will be passed to the handler during execution, 6) an optional wildcard parameter and 7) a series of expressions which are executed in order when the handler is called. The return value of a message handler is the evaluation of the last expression in the body.

Syntax

Defaults are outlined.


(defmessage-handler <class-name> <message-name>

[<handler-type>] [<comment>]

(<parameter>* [<wildcard-parameter>])

<action>*)


<handler-type> ::= around | before | primary | after

<parameter> ::= <single-field-variable>

<wildcard-parameter> ::= <multifield-variable>


Message handlers are uniquely identified by class, name and type. Message handlers are never called directly. When the user sends a message to an object, CLIPS selects and orders the applicable message handlers attached to the object’s class(es) and then executes them. This process is termed the message dispatch.

Example

CLIPS> (clear)

CLIPS> (defclass A (is-a USER) (role concrete))

CLIPS>

(defmessage-handler A delete before ()

(printout t “Deleting an instance of the class A…” crlf))

CLIPS>

(defmessage-handler USER delete after ()

(printout t “System completed deletion of an instance.”

crlf))

CLIPS> (watch instances)

CLIPS> (make-instance a of A)

==> instance [a] of A

[a]

CLIPS> (send [a] delete)

Deleting an instance of the class A…

⇐= instance [a] of A

System completed deletion of an instance.

TRUE

CLIPS> (unwatch instances)

CLIPS>

9.4.1 Message handler Parameters

A message handler may accept exactly or at least a specified number of arguments, depending on whether a wildcard parameter is used or not. The regular parameters specify the minimum number of arguments that must be passed to the handler. Each of these parameters may be referenced like a normal single field variable within the actions of the handler. If a wildcard parameter is present, the handler may be passed any number of arguments greater than or equal to the minimum. If no wildcard parameter is present, then the handler must be passed exactly the number of arguments specified by the regular parameters. All arguments to a handler that do not correspond to a regular parameter are grouped into a multifield value that can be referenced by the wildcard parameter. The standard CLIPS multifield functions, such as length$ and expand$, can be applied to the wildcard parameter.


Handler parameters have no bearing on the applicability of a handler to a particular message (see section 9.5.1). However, if the number of arguments is inappropriate, a message execution error (see section 9.5.4) will be generated when the handler is called. Thus, the number of arguments accepted should be consistent for all message handlers applicable to a particular message.

Example

CLIPS> (clear)

CLIPS>

(defclass CAR (is-a USER)

(role concrete)

(slot front-seat)

(multislot trunk)

(slot trunk-count))

CLIPS>

(defmessage-handler CAR put-items-in-car (?item $?rest)

(bind ?self:front-seat ?item)

(bind ?self:trunk ?rest)

(bind ?self:trunk-count (length$ ?rest)))

CLIPS> (make-instance Pinto of CAR)

[Pinto]

CLIPS> (send [Pinto] put-items-in-car bag-of-groceries

tire suitcase)

2

CLIPS> (send [Pinto] print)

[Pinto] of CAR

(front-seat bag-of-groceries)

(trunk tire suitcase)

(trunk-count 2)

CLIPS>

9.4.1.1 Active Instance Parameter

The term active instance refers to an instance which is responding to a message. All message handlers have an implicit parameter called ?self which binds the active instance for a message. This parameter name is reserved and cannot be explicitly listed in the message handler’s parameters, nor can it be rebound within the body of a message handler.

Example

CLIPS> (clear)

CLIPS> (defclass A (is-a USER) (role concrete))

CLIPS> (make-instance a of A)

[a]

CLIPS>

(defmessage-handler A print-args (?a ?b $?c)

(printout t (instance-name ?self) ” “ ?a ” “ ?b

” and “ (length$ ?c) ” extras: “ ?c crlf))

CLIPS> (send [a] print-args 1 2)

[a] 1 2 and 0 extras: ()

CLIPS> (send [a] print-args a b c d)

[a] a b and 2 extras: (c d)

CLIPS>

9.4.2 Message handler Actions

The body of a message handler is a sequence of expressions that are executed in order when the handler is called. The return value of the message handler is the result of the evaluation of the last expression in the body.


Handler actions may directly manipulate slots of the active instance. Normally, slots can only be manipulated by sending the object slot accessor messages (see sections 9.3.3.9 and 9.4.3). However, handlers are considered part of the encapsulation (see section 2.6.2) of an object, and thus can directly view and change the slots of the object. There are several functions which operate implicitly on the active instance (without the use of messages) and can only be called from within a message handler. These functions are discussed in section 12.16.


A shorthand notation is provided for accessing slots of the active instance from within a message handler.

Syntax

?self:<slot-name>

Example

CLIPS> (clear)

CLIPS>

(defclass A (is-a USER)

(role concrete)

(slot foo (default 1))

(slot bar (default 2)))

CLIPS>

(defmessage-handler A print-all-slots ()

(printout t ?self:foo ” “ ?self:bar crlf))

CLIPS> (make-instance a of A)

[a]

CLIPS> (send [a] print-all-slots)

1 2

CLIPS>


The bind function can also take advantage of this shorthand notation to set the value of a slot.

Syntax

(bind ?self:<slot-name> <value>*)

Example

CLIPS>

(defmessage-handler A set-foo (?value)

(bind ?self:foo ?value))

CLIPS> (send [a] set-foo 34)

34

CLIPS>


Direct slot accesses are statically bound to the appropriate slot in the defclass when the message handler is defined. Care must be taken when these direct slot accesses can be executed as the result of a message sent to an instance of a subclass of the class to which the message handler is attached. If the subclass has redefined the slot, the direct slot access contained in the message handler attached to the superclass will fail. That message handler accesses the slot in the superclass, not the subclass.

Example

CLIPS> (clear)

CLIPS>

(defclass A (is-a USER)

(slot foo (create-accessor read)))

CLIPS>

(defclass B (is-a A)

(role concrete)

(slot foo))

CLIPS> (make-instance b of B)

[b]

CLIPS> (send [b] get-foo)

[MSGPASS3] Static reference to slot foo of class A does not apply to [b] of B

[PRCCODE4] Execution halted during the actions of message-handler get-foo primary in class A

FALSE

CLIPS>


In order for direct slot accesses in a superclass message handler to apply to new versions of the slot in subclasses, the dynamic put and dynamic get (see sections 12.16.4.10 and 12.16.4.11) must be used. However, the subclass slot must have public visibility for this to work (see section 9.3.3.8).

Example

CLIPS> (clear)

CLIPS>

(defclass A (is-a USER)

(slot foo))

CLIPS>

(defmessage-handler A get-foo ()

(dynamic-get foo))

CLIPS>

(defclass B (is-a A)

(role concrete)

(slot foo (visibility public)))

CLIPS> (make-instance b of B)

[b]

CLIPS> (send [b] get-foo)

nil

CLIPS>

9.4.3 Daemons

Daemons are pieces of code which execute implicitly whenever some basic action is taken upon an instance, such as initialization, deletion, or reading and writing of slots. All these basic actions are implemented with primary handlers attached to the class of the instance. Daemons may be easily implemented by defining other types of message handlers, such as before or after, which will recognize the same messages. These pieces of code will then be executed whenever the basic actions are performed on the instance.

Example

CLIPS> (clear)

CLIPS> (defclass A (is-a USER) (role concrete))

CLIPS>

(defmessage-handler A init before ()

(printout t “Initializing a new instance of class A…”

crlf))

CLIPS> (make-instance a of A)

Initializing a new instance of class A…

[a]

CLIPS>

9.4.4 Predefined System Message handlers

CLIPS defines eight primary message handlers that are attached to the class USER. These handlers cannot be deleted or modified.

9.4.4.1 Instance Initialization

Syntax

(defmessage-handler USER init primary ())


This handler is responsible for initializing instances with class default values after creation. The make instance and initialize instance functions send the init message to an instance (see sections 9.6.1 and 9.6.2); the user should never send this message directly. This handler is implemented using the init slots function (see section 12.13). User defined init handlers should not prevent the system message handler from responding to an init message (see section 9.5.3).

Example

CLIPS> (clear)

CLIPS>

(defclass CAR (is-a USER)

(role concrete)

(slot price (default 75000))

(slot model (default Corniche)))

CLIPS> (watch messages)

CLIPS> (watch message-handlers)

CLIPS> (make-instance Rolls-Royce of CAR)

MSG » create ED:1 (<Instance-Rolls-Royce>)

HND » create primary in class USER

ED:1 (<Instance-Rolls-Royce>)

HND « create primary in class USER

ED:1 (<Instance-Rolls-Royce>)

MSG « create ED:1 (<Instance-Rolls-Royce>)

MSG » init ED:1 (<Instance-Rolls-Royce>)

HND » init primary in class USER

ED:1 (<Instance-Rolls-Royce>)

HND « init primary in class USER

ED:1 (<Instance-Rolls-Royce>)

MSG « init ED:1 (<Instance-Rolls-Royce>)

[Rolls-Royce]

CLIPS>

9.4.4.2 Instance Deletion

Syntax

(defmessage-handler USER delete primary ())


This handler is responsible for deleting an instance from the system. The user must directly send a delete message to an instance. User defined delete message handlers should not prevent the system message handler from responding to a delete message (see section 9.5.3). The handler returns the symbol TRUE if the instance was successfully deleted, otherwise it returns the symbol FALSE.

Example

CLIPS> (send [Rolls-Royce] delete)

MSG » delete ED:1 (<Instance-Rolls-Royce>)

HND » delete primary in class USER

ED:1 (<Instance-Rolls-Royce>)

HND « delete primary in class USER

ED:1 (<Stale Instance-Rolls-Royce>)

MSG « delete ED:1 (<Stale Instance-Rolls-Royce>)

TRUE

CLIPS>

9.4.4.3 Instance Display

Syntax

(defmessage-handler USER print primary ())


This handler prints out slots and their values for an instance.

Example

CLIPS> (make-instance Rolls-Royce of CAR)

MSG » create ED:1 (<Instance-Rolls-Royce>)

HND » create primary in class USER

ED:1 (<Instance-Rolls-Royce>)

HND « create primary in class USER

ED:1 (<Instance-Rolls-Royce>)

MSG « create ED:1 (<Instance-Rolls-Royce>)

MSG » init ED:1 (<Instance-Rolls-Royce>)

HND » init primary in class USER

ED:1 (<Instance-Rolls-Royce>)

HND « init primary in class USER

ED:1 (<Instance-Rolls-Royce>)

MSG « init ED:1 (<Instance-Rolls-Royce>)

[Rolls-Royce]

CLIPS> (send [Rolls-Royce] print)

MSG » print ED:1 (<Instance-Rolls-Royce>)

HND » print primary in class USER

ED:1 (<Instance-Rolls-Royce>)

[Rolls-Royce] of CAR

(price 75000)

(model Corniche)

HND « print primary in class USER

ED:1 (<Instance-Rolls-Royce>)

MSG « print ED:1 (<Instance-Rolls-Royce>)

CLIPS> (unwatch messages)

CLIPS. (unwatch message-handlers)

CLIPS>

9.4.4.4 Directly Modifying an Instance

Syntax

(defmessage-handler USER direct-modify primary

(?slot-override-expressions))


This handler modifies the slots of an instance directly rather than using put- override messages to place the slot values. The slot override expressions are passed as an EXTERNAL_ADDRESS data object to the direct modify handler. This message is used by the functions modify instance and active modify instance.

Example

The following around message handler could be used to insure that all modify message slot overrides are handled using put- messages.


(defmessage-handler USER direct-modify around

(?overrides)

(send ?self message-modify ?overrides))

9.4.4.5 Modifying an Instance using Messages

Syntax

(defmessage-handler USER message-modify primary

(?slot-override-expressions)


This handler modifies the slots of an instance using put  messages for each slot update. The slot override expressions are passed as an EXTERNAL_ADDRESS data object to the message modify handler. This message is used by the functions message modify instance and active message modify instance.

9.4.4.6 Directly Duplicating an Instance

Syntax

(defmessage-handler USER direct-duplicate primary

(?new-instance-name ?slot-override-expressions))



This handler duplicates an instance without using put- messages to assign the slot overrides. Slot values from the original instance and slot overrides are directly copied. If the name of the new instance created matches a currently existing instance name, then the currently existing instance is deleted without use of a message. The slot override expressions are passed as an EXTERNAL_ADDRESS data object to the direct duplicate handler. This message is used by the functions duplicate instance and active duplicate instance.

Example

The following around message handler could be used to insure that all duplicate message slot overrides are handled using put- messages.


(defmessage-handler USER direct-duplicate around

(?new-name ?overrides)

(send ?self message-duplicate ?new-name ?overrides))

9.4.4.7 Duplicating an Instance using Messages

Syntax

(defmessage-handler USER message-duplicate primary

(?new-instance-name ?slot-override-expressions)


This handler duplicates an instance using messages. Slot values from the original instance and slot overrides are copied using put  and get  messages. If the name of the new instance created matches a currently existing instance name, then the currently existing instance is deleted using a delete message. After creation, the new instance is sent a create message and then an init message. The slot override expressions are passed as an EXTERNAL_ADDRESS data object to the message duplicate handler. This message is used by the functions message duplicate instance and active message duplicate instance.

9.4.4.8 Instance Creation

Syntax

(defmessage-handler USER create primary ())


This handler is called after an instance is created , but before any slot initialization has occurred. The newly created instance is sent a create message. This handler performs no actions—It is provided so that instance creation can be detected by user-defined message-handlers. The handler returns the symbol TRUE if the instance was successfully created, otherwise it returns the symbol FALSE.

9.5 Message Dispatch

When a message is sent to an object using the send function, CLIPS examines the class precedence list of the active instance’s class to determine a complete set of message handlers which are applicable to the message. CLIPS uses the roles (around, before, primary or after) and specificity of these message handlers to establish an ordering and then executes them. A handler which is attached to a subclass of another message handler’s class is said to be more specific. This entire process is referred to as the message dispatch. Following is a flow diagram summary:


| |





The solid arrows indicate automatic control transfer by the message dispatch system.
The dashed arrows indicate control transfer that can only be accomplished by the use or lack of the use of call next handler (or override next handler). |

9.5.1 Applicability of Message handlers

A message handler is applicable to a message if its name matches the message, and it is attached to a class which is in the class precedence list of the class of the instance receiving the message.

9.5.2 Message handler Precedence

The set of all applicable message handlers are sorted into four groups according to role, and these four groups are further sorted by class specificity. The around, before and primary handlers are ordered from most specific to most general, whereas after handlers are ordered from most general to most specific.


The order of execution is as follows: 1) around handlers begin execution from most specific to most general (each around handler must explicitly allow execution of other handlers), 2) before handlers execute (one after the other) from most specific to most general 3) primary handlers begin execution from most specific to most general (more specific primary handlers must explicitly allow execution of more general ones), 4) primary handlers finish execution from most general to most specific, 5) after handlers execute (one after the other) from most general to most specific and 6) aroundhandlers finish execution from most general to most specific.


There must be at least one applicable primary handler for a message, or a message execution error will be generated (see section 9.5.4).

9.5.3 Shadowed Message handlers

When one handler must be called by another handler in order to be executed, the first handler is said to be shadowed by the second. An around handler shadows all handlers except more specific around handlers. A primary handler shadows all more general primary handlers.


Messages should be implemented using the declarative technique, if possible. Only the handler roles will dictate which handlers get executed; only before and after handlers and the most specific primaryhandler are used. This allows each handler for a message to be completely independent of the other message handlers. However, if around handlers or shadowed primary handlers are necessary, then the handlers must explicitly take part in the message dispatch by calling other handlers they are shadowing. This is called the imperative technique. The functions call next handlerand override next handler (see section 12.16.2) allow a handler to execute the handler it is shadowing. A handler can call the same shadowed handler multiple times.

Example

(defmessage-handler USER my-message around () (call-next-handler)) (defmessage-handler USER my-message before ()) (defmessage-handler USER my-message () (call-next-handler)) (defmessage-handler USER my-message after ()) (defmessage-handler OBJECT my-message around () (call-next-handler)) (defmessage-handler OBJECT my-message before ()) (defmessage-handler OBJECT my-message ()) (defmessage-handler OBJECT my-message after ())
For a message sent to an instance of a class which inherits from USER, the diagram to the right illustrates the order of execution for the handlers attached to the classes USER and OBJECT. The brackets indicate where a particular handler begins and ends execution. Handlers enclosed within a bracket are shadowed.


9.5.4 Message Execution Errors

If an error occurs at any time during the execution of a message handler, any currently executing handlers will be aborted, any handlers which have not yet started execution will be ignored, and the sendfunction will return the symbol FALSE.


A lack of applicable of primary message handlers and a handler being called with the wrong number of arguments are common message execution errors.

9.5.5 Message Return Value

The return value of call to the send function is the return value of the most specific around handler, or the most specific primary handler if there are no around handlers. The return value of a handler is the result of the evaluation of the last action in the handler.


The return values of the before and after handlers are ignored; they are for side effects only. An around handler can choose to ignore or capture the return value of the next most specific around or primary handler. A primary handler can choose to ignore or capture the return value of a more general primary handler.

9.6 Manipulating Instances

Objects are manipulated by sending them messages. This is achieved by using the send function, which takes as arguments the destination object for the message, the message itself and any arguments which are to be passed to handlers.

Syntax

(send <object-expression>

<message-name-expression> <expression>*)


Section 2.4.2 explains object references. The return value of send is the result of the message as explained in section 9.5.5.


The slots of an object may be read or set directly only within the body of a message handler that is executing on behalf of a message that was sent to that object. This is how COOL implements the notion of encapsulation (see Section 2.6.2). Any action performed on an object by an external source, such as a rule or function, must be done with messages. There are two major exceptions: 1) objects which are not instances of user defined classes (floating point and integer numbers, symbols, strings, multifield values, fact addresses and external addresses) can be manipulated in the standard non OOP manner of previous versions of CLIPS as well and 2) creation and initialization of an instance of a user defined class are performed via the function make instance.

9.6.1 Creating Instances

Like facts, instances of user defined classes must be explicitly created by the user. Likewise, all instances are deleted during the resetcommand, and they can be loaded and saved similarly to facts. All operations involving instances require message passing using the send function except for creation, since the object does not yet exist. A function called make instance is used to create and initialize a new instance. This function implicitly sends first a create message and then an initialization message to the new object after allocation. The user can customize instance initialization with daemons. make instance also allows slot overrides to change any predefined initialization for a particular instance. make instance automatically delays all object pattern matching activities for rules until all slot overrides have been processed. The function active make instance can be used if delayed pattern matching is not desired. active make instance remembers the current state of delayed pattern matching, explicitly turns delay on, and then restores it to its previous state once all slot overrides have been processed.

Syntax

(make-instance <instance-definition>)

(active-make-instance <instance-definition>)


<instance-definition> ::= [<instance-name-expression>] of

<class-name-expression>

<slot-override>*

<slot-override> ::= (<slot-name-expression> <expression>*)


The return value of make instance is the name of the new instance on success or the symbol FALSE on failure. The evaluation of <instance name expression> can either be an instance name or a symbol. If <instance name expression> is not specified, then the function gensym* will be called to generate the instance name.


make instance performs the following steps in order:


1) If an instance of the specified name already exists, that instance receives a delete message, e.g. (send <instance name> delete). If this fails for any reason, the new instance creation is aborted. Normally, the handler attached to class USER will respond to this message (see section 9.4.5.2).

2) A new and uninitialized instance of the specified class is created with the specified name.

3) The new instance receives the create message, e.g. (send <instance name> create). Normally, the handler attached to class USER will respond to this message (see section 9.4.4.8), although it performs no actions.

4) All slot overrides are immediately evaluated and placed via put messages (see section 9.3.3.10), e.g. (send <instance name> put <slot name> <expression>*). If there are any errors, the new instance is deleted.

5) The new instance receives the init message, e.g. (send <instance name> init). Normally, the handler attached to class USER will respond to this message (see section 9.4.4.1). This handler calls the init slots function (see section 12.16.4.1). This function uses defaults from the class definition (if any) for any slots which do not have slot overrides. The class defaults are placed directly without the use of messages. If there are any errors, the new instance is deleted.

Example

CLIPS> (clear)

CLIPS>

(defclass A (is-a USER)

(role concrete)

(slot x (default 34)

(create-accessor write))

(slot y (default abc)))

CLIPS>

(defmessage-handler A put-x before (?value)

(printout t “Slot x set with message.” crlf))

CLIPS>

(defmessage-handler A delete after ()

(printout t “Old instance deleted.” crlf))

CLIPS> (make-instance a of A)

[a]

CLIPS> (send [a] print)

[a] of A

(x 34)

(y abc)

CLIPS> (make-instance [a] of A (x 65))

Old instance deleted.

Slot x set with message.

[a]

CLIPS> (send [a] print)

a of A

(x 65)

(y abc)

CLIPS> (send [a] delete)

Old instance deleted.

TRUE

CLIPS>

9.6.1.1 Definstances Construct

Similar to deffacts, the definstances construct allows the specification of instances which will be created every time the reset command is executed. On every reset all current instances receive a delete message, and the equivalent of a make instancefunction call is made for every instance specified in definstances constructs.

Syntax

(definstances <definstances-name> [active] [<comment>]

<instance-template>*)

<instance-template> ::= (<instance-definition>)


A definstances cannot use classes which have not been previously defined. The instances of a definstances are created in order, and if any individual creation fails, the remainder of the definstances will be aborted. Normally, definstances just use the make instance function (which means delayed Rete activity) to create the instances. However, if this is not desired,then the active keyword can be specified after the definstances name so that the active make instance function will be used.

Example

CLIPS> (clear)

CLIPS>

(defclass A (is-a USER) (role concrete)

(slot x (create-accessor write) (default 1)))

CLIPS>

(definstances A-OBJECTS

(a1 of A)

(of A (x 65)))

CLIPS> (watch instances)

CLIPS> (reset)

==> instance [initial-object] of INITIAL-OBJECT

==> instance [a1] of A

==> instance [gen1] of A

CLIPS> (reset)

⇐= instance [initial-object] of INITIAL-OBJECT

⇐= instance [a1] of A

⇐= instance [gen1] of A

==> instance [initial-object] of INITIAL-OBJECT

==> instance [a1] of A

==> instance [gen2] of A

CLIPS> (unwatch instances)

CLIPS>


Upon startup and after a clear command, CLIPS automatically constructs the following definstances.


(definstances initial-object

(initial-object of INITIAL-OBJECT))


The class INITIAL-OBJECT is a predefined system class that is a direct subclass of USER.


(defclass INITIAL-OBJECT

(is-a USER)

(role concrete)

(pattern-match reactive))


The initial object definstances and the INITIAL OBJECT class are only defined if both the object system and defrules are enabled (see section 2 of the Advanced Programming Guide). The INITIAL OBJECT class cannot be deleted, but the initial object definstances can. See section 5.4.9 for details on default patterns which pattern match against the initial object instance.

9.6.2 Reinitializing Existing Instances

The initialize instance function provides the ability to reinitialize an existing instance with class defaults and new slot overrides. The return value of initialize instance is the name of the instance on success or the symbol FALSE on failure. The evaluation of <instance name expression> can either be an instance name, instance address or a symbol. initialize instance automatically delays all object pattern matching activities for rules until all slot overrides have been processed. The function active initialize instance can be used if delayed pattern matching is not desired.

Syntax

(initialize-instance <instance-name-expression>

<slot-override>*)


initialize instance performs the following steps in order:


1) All slot overrides are immediately evaluated and placed via put  messages (see section 9.3.3.10), e.g. (send <instance name> put <slot name> <expression>*).

2) The instance receives the init message, e.g. (send <instance name> init). Normally, the handler attached to class USER will respond to this message (see section 9.4.5.1). This handler calls the init slots function (see section 12.16.4.1). This function uses defaults from the class definition (if any) for any slots which do not have slot overrides. The class defaults are placed directly without the use of messages.


If no slot override or class default specifies the value of a slot, that value will remain the same. Empty class default values allow initialize instance to clear a slot.


If an error occurs, the instance will not be deleted, but the slot values may be in an inconsistent state.

Example

CLIPS> (clear)

CLIPS>

(defclass A (is-a USER)

(role concrete)

(slot x (default 34)

(create-accessor write))

(slot y (default ?NONE)

(create-accessor write))

(slot z (create-accessor write)))

CLIPS> (make-instance a of A (y 100))

[a]

CLIPS> (send [a] print)

[a] of A

(x 34)

(y 100)

(z nil)

CLIPS> (send [a] put-x 65)

65

CLIPS> (send [a] put-y abc)

abc

CLIPS> (send [a] put-z “Hello world.”)

“Hello world.”

CLIPS> (send [a] print)

[a] of A

(x 65)

(y abc)

(z “Hello world.”)

CLIPS> (initialize-instance a)

[a]

CLIPS> (send [a] print)

a of A

(x 34)

(y abc)

(z nil)

CLIPS>

9.6.3 Reading Slots

Sources external to an object, such as a rule or deffunction, can read an object’s slots only by sending the object a message. Message handlers executing on the behalf of an object can either use messages or direct access to read the object’s slots (see section 9.4.2). Several functions also exist which operate implicitly on the active instance for a message that can only be called by message handlers, such as dynamic get (see section 12.16.4.10).


Section 12.16 describes ways of testing for the existence of slots and their values.

Example

CLIPS> (clear)

CLIPS>

(defclass A (is-a USER)

(role concrete)

(slot x (create-accessor read)

(default abc)))

CLIPS> (make-instance a of A)

[a]

CLIPS> (sym-cat (send [a] get-x) def)

abcdef

CLIPS>

9.6.4 Setting Slots

Sources external to an object, such as a rule or deffunction, can write an object’s slots only by sending the object a message. Several functions also exist which operate implicitly on the active instance for a message that can only be called by message handlers, such as dynamic put (see section 12.16.4.11). The bind function can also be used to set a slot's value from within a message handler (see section 9.4.2).

Example

CLIPS> (clear)

CLIPS>

(defclass A (is-a USER)

(role concrete)

(slot x (create-accessor write)

(default abc)))

CLIPS> (make-instance a of A)

[a]

CLIPS> (send [a] put-x “New value.”)

“New value.”

CLIPS>

9.6.5 Deleting Instances

Sending the delete message to an instance removes it from the system. Within a message handler, the delete instance function (see section 12.16) can be used to delete the active instance for a message.

Syntax

(send <instance> delete)

9.6.6 Delayed Pattern Matching When Manipulating Instances

While manipulating instances (either by creating, modifying, or deleting), it is possible to delay pattern matching activities for rules until after all of the manipulations have been made. This can be accomplished using the object pattern match delay function. This function acts identically to the progn function, however, any actions which could affect object pattern matching for rules are delayed until the function is exited. This function’s primary purpose is to provide some control over performance.

Syntax

(object-pattern-match-delay <action>*)

Example

CLIPS> (clear)

CLIPS>

(defclass A (is-a USER)

(role concrete)

(pattern-match reactive))

CLIPS>

(defrule match-A

(object (is-a A))

⇒)

CLIPS> (make-instance a of A)

[a]

CLIPS> (agenda)

0 match-A: [a]

For a total of 1 activation.

CLIPS> (make-instance b of A)

[b]

CLIPS> (agenda)

0 match-A: [b]

0 match-A: [a]

For a total of 2 activations.

CLIPS>

(object-pattern-match-delay

(make-instance c of A)

(printout t “After c…” crlf)

(agenda)

(make-instance d of A)

(printout t “After d…” crlf)

(agenda))

After c…

0 match-A: [b]

0 match-A: [a]

For a total of 2 activations.

After d…

0 match-A: [b]

0 match-A: [a]

For a total of 2 activations.

CLIPS> (agenda)

0 match-A: [d]

0 match-A: [c]

0 match-A: [b]

0 match-A: [a]

For a total of 4 activations.

CLIPS>

9.6.7 Modifying Instances

Four functions are provided for modifying instances. These functions allow instance slot updates to be performed in blocks without requiring a series of put  messages. Each of these functions returns the symbol TRUE if successful, otherwise the symbol FALSE is returned.

9.6.7.1 Directly Modifying an Instance with Delayed Pattern Matching

The modify instance function uses the direct modify message to change the values of the instance. Object pattern matching is delayed until all of the slot modifications have been performed.

Syntax

(modify-instance <instance> <slot-override>*)

Example

CLIPS> (clear)

CLIPS>

(defclass A (is-a USER)

(role concrete)

(slot foo)

(slot bar))

CLIPS> (make-instance a of A)

[a]

CLIPS> (watch all)

CLIPS> (modify-instance a (foo 0))

MSG » direct-modify ED:1 (<Instance-a> <Pointer-0019CD5A>)

HND » direct-modify primary in class USER.

ED:1 (<Instance-a> <Pointer-0019CD5A>)

::= local slot foo in instance a ← 0

HND « direct-modify primary in class USER.

ED:1 (<Instance-a> <Pointer-0019CD5A>)

MSG « direct-modify ED:1 (<Instance-a> <Pointer-0019CD5A>)

TRUE

CLIPS> (unwatch all)

CLIPS>

9.6.7.2 Directly Modifying an Instance with Immediate Pattern Matching

The active modify instance function uses the direct modify message to change the values of the instance. Object pattern matching occurs as slot modifications are being performed.

Syntax

(active-modify-instance <instance> <slot-override>*)

9.6.7.3 Modifying an Instance using Messages with Delayed Pattern Matching

The message modify instance function uses the message modify message to change the values of the instance. Object pattern matching is delayed until all of the slot modifications have been performed.

Syntax

(message-modify-instance <instance> <slot-override>*)

Example

CLIPS> (clear)

CLIPS>

(defclass A (is-a USER)

(role concrete)

(slot foo)

(slot bar (create-accessor write)))

CLIPS> (make-instance a of A)

[a]

CLIPS> (watch all)

CLIPS> (message-modify-instance a (bar 4))

MSG » message-modify ED:1 (<Instance-a> <Pointer-009F04A0>)

HND » message-modify primary in class USER

ED:1 (<Instance-a> <Pointer-009F04A0>)

MSG » put-bar ED:2 (<Instance-a> 4)

HND » put-bar primary in class A

ED:2 (<Instance-a> 4)

::= local slot bar in instance a ← 4

HND « put-bar primary in class A

ED:2 (<Instance-a> 4)

MSG « put-bar ED:2 (<Instance-a> 4)

HND « message-modify primary in class USER

ED:1 (<Instance-a> <Pointer-009F04A0>)

MSG « message-modify ED:1 (<Instance-a> <Pointer-009F04A0>)

TRUE

CLIPS> (unwatch all)

CLIPS>

9.6.7.4 Modifying an Instance using Messages with Immediate Pattern Matching

The active message modify instance function uses the message modify message to change the values of the instance. Object pattern matching occurs as slot modifications are being performed.

Syntax

(active-message-modify-instance <instance> <slot-override>*)

9.6.8 Duplicating Instances

Four functions are provided for duplicating instances. These functions allow instance duplication and slot updates to be performed in blocks without requiring a series of put  messages. Each of these functions return the instance name of the new duplicated instance if successful, otherwise the symbol FALSE is returned.


Each of the duplicate functions can optionally specify the name of the instance to which the old instance will be copied. If the name is not specified, the function will generate the name using the (gensym*) function. If the target instance already exists, it will be deleted directly or with a delete message depending on which function was called.

9.6.8.1 Directly Duplicating an Instance with Delayed Pattern Matching

The duplicate instance function uses the direct duplicate message to change the values of the instance. Object pattern matching is delayed until all of the slot modifications have been performed.

Syntax

(duplicate-instance <instance> [to <instance name>]

<slot-override>*)

Example

CLIPS> (clear)

CLIPS> (setgen 1)

1

CLIPS>

(defclass A (is-a USER)

(role concrete)

(slot foo (create-accessor write))

(slot bar (create-accessor write)))

CLIPS> (make-instance a of A (foo 0) (bar 4))

[a]

CLIPS> (watch all)

CLIPS> (duplicate-instance a)

MSG » direct-duplicate ED:1 (<Instance-a> [gen1] <Pointer-00000000>)

HND » direct-duplicate primary in class USER

ED:1 (<Instance-a> [gen1] <Pointer-00000000>)

==> instance [gen1] of A

::= local slot foo in instance gen1 ← 0

::= local slot bar in instance gen1 ← 4

HND « direct-duplicate primary in class USER

ED:1 (<Instance-a> [gen1] <Pointer-00000000>)

MSG « direct-duplicate ED:1 (<Instance-a> [gen1] <Pointer-00000000>)

[gen1]

CLIPS> (unwatch all)

CLIPS>

9.6.8.2 Directly Duplicating an Instance with Immediate Pattern Matching

The active duplicate instance function uses the direct duplicate message to change the values of the instance. Object pattern matching occurs as slot modifications are being performed.

Syntax

(active-duplicate-instance <instance> [to <instance name>]

<slot-override>*)

9.6.8.3 Duplicating an Instance using Messages with Delayed Pattern Matching

The message duplicate instance function uses the message duplicate message to change the values of the instance. Object pattern matching is delayed until all of the slot modifications have been performed.

Syntax

(message-duplicate-instance <instance> [to <instance name>]

<slot-override>*)

Example

CLIPS> (clear)

CLIPS>

(defclass A (is-a USER)

(role concrete)

(slot foo (create-accessor write))

(slot bar (create-accessor write)))

CLIPS> (make-instance a of A (foo 0) (bar 4))

[a]

CLIPS> (make-instance b of A)

[b]

CLIPS> (watch all)

CLIPS> (message-duplicate-instance a to b (bar 6))

MSG » message-duplicate ED:1 (<Instance-a> [b] <Pointer-009F04A0>)

HND » message-duplicate primary in class USER

ED:1 (<Instance-a> [b] <Pointer-009F04A0>)

MSG » delete ED:2 (<Instance-b>)

HND » delete primary in class USER

ED:2 (<Instance-b>)

⇐= instance [b] of A

HND « delete primary in class USER

ED:2 (<Stale Instance-b>)

MSG « delete ED:2 (<Stale Instance-b>)

==> instance [b] of A

MSG » create ED:2 (<Instance-b>)

HND » create primary in class USER

ED:2 (<Instance-b>)

HND « create primary in class USER

ED:2 (<Instance-b>)

MSG « create ED:2 (<Instance-b>)

MSG » put-bar ED:2 (<Instance-b> 6)

HND » put-bar primary in class A

ED:2 (<Instance-b> 6)

::= local slot bar in instance b ← 6

HND « put-bar primary in class A

ED:2 (<Instance-b> 6)

MSG « put-bar ED:2 (<Instance-b> 6)

MSG » put-foo ED:2 (<Instance-b> 0)

HND » put-foo primary in class A

ED:2 (<Instance-b> 0)

::= local slot foo in instance b ← 0

HND « put-foo primary in class A

ED:2 (<Instance-b> 0)

MSG « put-foo ED:2 (<Instance-b> 0)

MSG » init ED:2 (<Instance-b>)

HND » init primary in class USER

ED:2 (<Instance-b>)

HND « init primary in class USER

ED:2 (<Instance-b>)

MSG « init ED:2 (<Instance-b>)

HND « message-duplicate primary in class USER

ED:1 (<Instance-a> [b] <Pointer-009F04A0>)

MSG « message-duplicate ED:1 (<Instance-a> [b] <Pointer-009F04A0>)

[b]

CLIPS> (unwatch all)

CLIPS>

9.6.8.4 Duplicating an Instance using Messages with Immediate Pattern Matching

The active message duplicate instance function uses the message duplicate message to change the values of the instance. Object pattern matching occurs as slot modifications are being performed.

Syntax

(active-message-duplicate-instance <instance>

[to <instance name>]

<slot-override>*)


9.7 Instance set Queries and Distributed Actions

COOL provides a useful query system for determining and performing actions on sets of instances of user defined classes that satisfy user defined queries. The instance query system in COOL provides six functions, each of which operate on instance sets determined by user defined criteria:


| Function | Purpose |

any-instancep Determines if one or more instance sets satisfy a query
find-instance Returns the first instance set that satisfies a query
find-all-instances Groups and returns all instance sets which satisfy a query
do-for-instance Performs an action for the first instance set which satisfies a query
do-for-all-instances Performs an action for every instance set which satisfies a query as they are found
delayed do for all instances Groups all instance sets which satisfy a query and then iterates an action over this group


Explanations on how to form instance set templates, queries and actions immediately follow, for these definitions are common to all of the query functions. The specific details of each query function will then be given. The following is a complete example of an instance set query function:

Example



For all of the examples in this section, assume that the commands below have already been entered:

Example

CLIPS>

(defclass PERSON (is-a USER)

(role abstract)

(slot sex (access read-only)

(storage shared))

(slot age (type NUMBER)

(visibility public)))

CLIPS>

(defmessage-handler PERSON put-age (?value)

(dynamic-put age ?value))

CLIPS>

(defclass FEMALE (is-a PERSON)

(role abstract)

(slot sex (source composite)

(default female)))

CLIPS>

(defclass MALE (is-a PERSON)

(role abstract)

(slot sex (source composite)

(default male)))

CLIPS>

(defclass GIRL (is-a FEMALE)

(role concrete)

(slot age (source composite)

(default 4)

(range 0.0 17.9)))

CLIPS>

(defclass WOMAN (is-a FEMALE)

(role concrete)

(slot age (source composite)

(default 25)

(range 18.0 100.0)))

CLIPS>

(defclass BOY (is-a MALE)

(role concrete)

(slot age (source composite)

(default 4)

(range 0.0 17.9)))

CLIPS>

(defclass MAN (is-a MALE)

(role concrete)

(slot age (source composite)

(default 25)

(range 18.0 100.0)))

CLIPS>

(definstances PEOPLE

(Man-1 of MAN (age 18))

(Man-2 of MAN (age 60))

(Woman-1 of WOMAN (age 18))

(Woman-2 of WOMAN (age 60))

(Woman-3 of WOMAN)

(Boy-1 of BOY (age 8))

(Boy-2 of BOY)

(Boy-3 of BOY)

(Boy-4 of BOY)

(Girl-1 of GIRL (age 8))

(Girl-2 of GIRL))

CLIPS> (reset)

CLIPS>

9.7.1 Instance set Definition

An instance set is an ordered collection of instances. Each instance set member is an instance of a set of classes, called class restrictions, defined by the user. The class restrictions can be different for each instance set member. The query functions use instance set templates to generate instance sets. An instance set template is a set of instance set member variables and their associated class restrictions. Instance set member variables reference the corresponding members in each instance set which matches a template. Variables may be used to specify the classes for the instance set template, but if the constant names of the classes are specified, the classes must already be defined. Module specifiers may be included with the class names; the classes need not be in scope of the current module.

Syntax

<instance-set-template>

::= (<instance-set-member-template>+)

<instance-set-member-template>

::= (<instance-set-member-variable> <class-restrictions>)

<instance-set-member-variable> ::= <single-field-variable>

<class-restrictions> ::= <class-name-expression>+

Example

One instance set template might be the ordered pairs of boys or men and girls or women.


((?man-or-boy BOY MAN) (?woman-or-girl GIRL WOMAN))


This instance set template could have been written equivalently:


((?man-or-boy MALE) (?woman-or-girl FEMALE))


Instance set member variables (e.g. ?man or boy) are bound to instance names.

9.7.2 Instance set Determination

COOL uses straightforward permutations to generate instance sets that match an instance set template from the actual instances in the system. The rules are as follows:


1) When there is more than one member in an instance set template, vary the rightmost members first.

2) When there is more than one class that an instance set member can be, iterate through the classes from left to right.

3) Examine instances of a class in the order that they were defined.

3a) Recursively examine instances of subclasses in the order that the subclasses were defined. If the specified query class was in scope of the current module, then only subclasses which are also in scope will be examined. Otherwise, only subclasses which are in scope of the module to which the query class belongs will be examined.

Example

For the instance set template given in section 9.7.1, thirty instance sets would be generated in the following order:


| 1. [Boy-1] [Girl-1] 2. [Boy-1] [Girl-2] 3. [Boy-1] [Woman-1] 4. [Boy-1] [Woman-2] 5. [Boy-1] [Woman-3] 6. [Boy-2] [Girl-1] 7. [Boy-2] [Girl-2] 8. [Boy-2] [Woman-1] 9. [Boy-2] [Woman-2] 10. [Boy-2] [Woman-3] 11. [Boy-3] [Girl-1] 12. [Boy-3] [Girl-2] 13 [Boy-3] [Woman-1] 14. [Boy-3] [Woman-2] 15. [Boy-3] [Woman-3]
| 16. [Boy-4] [Girl-1] 17. [Boy-4] [Girl-2] 18. [Boy-4] [Woman-1] 19. [Boy-4] [Woman-2] 20. [Boy-4] [Woman-3] 21. [Man-1] [Girl-1] 22. [Man-1] [Girl-2] 23. [Man-1] [Woman-1] 24. [Man-1] [Woman-2] 25. [Man-1] [Woman-3] 26. [Man-2] [Girl-1] 27. [Man-2] [Girl-2] 28. [Man-2] [Woman-1] 29. [Man-2] [Woman-2] 30. [Man-2] [Woman-3]
|

Example

Consider the following instance set template:


((?f1 FEMALE) (?f2 FEMALE))


Twenty five instance sets would be generated in the following order:


| 1. [Girl-1] [Girl-1] 2. [Girl-1] [Girl-2] 3. [Girl-1] [Woman-1] 4. [Girl-1] [Woman-2] 5. [Girl-1] [Woman-3] 6. [Girl-2] [Girl-1] 7. [Girl-2] [Girl-2] 8. [Girl-2] [Woman-1] 9. [Girl-2] [Woman-2] 10.[Girl-2] [Woman-3] 11.[Woman-1] [Girl-1] 12.[Woman-1] [Girl-2] 13.[Woman-1] [Woman-1] | 14.[Woman-1] [Woman-2] 15.[Woman-1] [Woman-3] 16.[Woman-2] [Girl-1] 17.[Woman-2] [Girl-2] 18.[Woman-2] [Woman-1] 19.[Woman-2] [Woman-2] 20.[Woman-2] [Woman-3] 21.[Woman-3] [Girl-1] 22.[Woman-3] [Girl-2] 23.[Woman-3] [Woman-1] 24.[Woman-3] [Woman-2] 25.[Woman-3] [Woman-3] |


The instances of class GIRL are examined before the instances of class WOMAN because GIRL was defined before WOMAN.

9.7.3 Query Definition

A query is a user defined boolean expression applied to an instance set to determine if the instance set meets further user defined restrictions. If the evaluation of this expression for an instance set is anything but the symbol FALSE, the instance set is said to satisfy the query.

Syntax

<query> ::= <boolean-expression>

Example

Continuing the previous example, one query might be that the two instances in an ordered pair have the same age.


(= (send ?man-or-boy get-age) (send ?woman-or-girl get-age))


Within a query, slots of instance set members can be directly read with a shorthand notation similar to that used in message handlers (see section 9.4.2). If message passing is not explicitly required for reading a slot (i.e. there are no accessor daemons for reads), then this second method of slot access should be used, for it gives a significant performance benefit.

Syntax

<instance-set-member-variable>:<slot-name>

Example

The previous example could be rewritten as:


(= ?man-or-boy:age ?woman-or-girl:age)


Since only instance sets which satisfy a query are of interest, and the query is evaluated for all possible instance sets, the query should not have any side effects.

9.7.4 Distributed Action Definition

A distributed action is a user defined expression evaluated for each instance set which satisfies a query. Unlike queries, distributed actions must use messages to read slots of instance set members. If more than one action is required, use the progn function (see section 12.6.5) to group them.

Action Syntax

<action> ::= <expression>

Example

Continuing the previous example, one distributed action might be to simply print out the ordered pair to the screen.


(printout t ”(“ ?man-or-boy ”,“ ?woman-or-girl ”)“ crlf)

9.7.5 Scope in Instance set Query Functions

An instance set query function can be called from anywhere that a regular function can be called. If a variable from an outer scope is not masked by an instance set member variable, then that variable may be referenced within the query and action. In addition, rebinding variables within an instance set function action is allowed. However, attempts to rebind instance set member variables will generate errors. Binding variables is not allowed within a query. Instance set query functions can be nested.

Example

CLIPS>

(deffunction count-instances (?class)

(bind ?count 0)

(do-for-all-instances ((?ins ?class)) TRUE

(bind ?count (+ ?count 1)))

?count)

CLIPS>

(deffunction count-instances-2 (?class)

(length (find-all-instances ((?ins ?class)) TRUE)))

CLIPS> (count-instances WOMAN)

3

CLIPS> (count-instances-2 BOY)

4

CLIPS>


Instance set member variables are only in scope within the instance set query function. Attempting to use instance set member variables in an outer scope will generate an error.

Example

CLIPS>

(deffunction last-instance (?class)

(any-instancep ((?ins ?class)) TRUE)

?ins)


[PRCCODE3] Undefined variable ins referenced in deffunction.


ERROR:

(deffunction last-instance

(?class)

(any-instancep ((?ins ?class))

TRUE)

?ins

)

CLIPS>

9.7.6 Errors during Instance set Query Functions

If an error occurs during an instance set query function, the function will be immediately terminated and the return value will be the symbol FALSE.

9.7.7 Halting and Returning Values from Query Functions

The functions break and return are now valid inside the action of the instance set query functions do for instance, do for all instances and delayed do for all instances. The return function is only valid if it is applicable in the outer scope, whereas the break function actually halts the query.

9.7.8 Instance set Query Functions

The instance query system in COOL provides six functions. For a given set of instances, all six query functions will iterate over these instances in the same order (see section 9.7.2). However, if a particular instance is deleted and recreated, the iteration order will change.

9.7.8.1 Testing if Any Instance set Satisfies a Query

This function applies a query to each instance set which matches the template. If an instance set satisfies the query, then the function is immediately terminated, and the return value is the symbol TRUE. Otherwise, the return value is the symbol FALSE.

Syntax

(any instancep <instance-set-template> <query>)

Example

Are there any men over age 30?


CLIPS> (any-instancep ((?man MAN)) (> ?man:age 30))

TRUE

CLIPS>

9.7.8.2 Determining the First Instance set Satisfying a Query

This function applies a query to each instance set which matches the template. If an instance set satisfies the query, then the function is immediately terminated, and the instance set is returned in a multifield value. Otherwise, the return value is a zero length multifield value. Each field of the multifield value is an instance name representing an instance set member.

Syntax

(find instance <instance-set-template> <query>)

Example

Find the first pair of a man and a woman who have the same age.


CLIPS>

(find-instance ((?m MAN) (?w WOMAN)) (= ?m:age ?w:age))

([Man-1] [Woman-1])

CLIPS>

9.7.8.3 Determining All Instance sets Satisfying a Query

This function applies a query to each instance set which matches the template. Each instance set which satisfies the query is stored in a multifield value. This multifield value is returned when the query has been applied to all possible instance sets. If there are n instances in each instance set, and m instance sets satisfied the query, then the length of the returned multifield value will be n * m. The first n fields correspond to the first instance set, and so on. Each field of the multifield value is an instance name representing an instance set member. The multifield value can consume a large amount of memory due to permutational explosion, so this function should be used judiciously.

Syntax

(find all instances <instance-set-template> <query>)

Example

Find all pairs of a man and a woman who have the same age.


CLIPS>

(find-all-instances ((?m MAN) (?w WOMAN)) (= ?m:age ?w:age))

([Man-1] [Woman-1] [Man-2] [Woman-2])

CLIPS>

9.7.8.4 Executing an Action for the First Instance set Satisfying a Query

This function applies a query to each instance set which matches the template. If an instance set satisfies the query, the specified action is executed, and the function is immediately terminated. The return value is the evaluation of the action. If no instance set satisfied the query, then the return value is the symbol FALSE.

Syntax

(do for instance <instance-set-template> <query> <action>*)

Example

Print out the first triplet of different people that have the same age. The calls to neq in the query eliminate the permutations where two or more members of the instance set are identical.


CLIPS>

(do-for-instance ((?p1 PERSON) (?p2 PERSON) (?p3 PERSON))

(and (= ?p1:age ?p2:age ?p3:age)

(neq ?p1 ?p2)

(neq ?p1 ?p3)

(neq ?p2 ?p3))

(printout t ?p1 ” “ ?p2 ” “ ?p3 crlf))

[Girl-2] [Boy-2] [Boy-3]

CLIPS>

9.7.8.5 Executing an Action for All Instance sets Satisfying a Query

This function applies a query to each instance set which matches the template. If an instance set satisfies the query, the specified action is executed. The return value is the evaluation of the action for the last instance set which satisfied the query. If no instance set satisfied the query, then the return value is the symbol FALSE.

Syntax

(do for all instances <instance-set-template> <query> <action>*)

Example

Print out all triplets of different people that have the same age. The calls to str compare limit the instance sets which satisfy the query to combinations instead of permutations. Without these restrictions, two instance sets which differed only in the order of their members would both satisfy the query.


CLIPS>

(do-for-all-instances ((?p1 PERSON) (?p2 PERSON) (?p3 PERSON))

(and (= ?p1:age ?p2:age ?p3:age)

(> (str-compare ?p1 ?p2) 0)

(> (str-compare ?p2 ?p3) 0))

(printout t ?p1 ” “ ?p2 ” “ ?p3 crlf))

[Girl-2] [Boy-3] [Boy-2]

[Girl-2] [Boy-4] [Boy-2]

[Girl-2] [Boy-4] [Boy-3]

[Boy-4] [Boy-3] [Boy-2]

CLIPS>

9.7.8.6 Executing a Delayed Action for All Instance setsSatisfying a Query

This function is similar to do for all instances except that it groups all instance sets which satisfy the query into an intermediary multifield value. If there are no instance sets which satisfy the query, then the function returns the symbol FALSE. Otherwise, the specified action is executed for each instance set in the multifield value, and the return value is the evaluation of the action for the last instance set to satisfy the query. The intermediary multifield value is discarded. This function can consume large amounts of memory in the same fashion as find all instances. This function should be used in lieu of do for all instances when the action applied to one instance set would change the result of the query for another instance set (unless that is the desired effect).

Syntax

(delayed do for all instances <instance-set-template>

<query> <action>*)

Example

Delete all boys with the greatest age. The test in this case is another query function which determines if there are any older boys than the one currently being examined. The action needs to be delayed until all boys have been processed, or the greatest age will decrease as the older boys are deleted.


CLIPS> (watch instances)

CLIPS>

(delayed-do-for-all-instances ((?b1 BOY))

(not (any-instancep ((?b2 BOY))

(> ?b2:age ?b1:age)))

(send ?b1 delete))

⇐= instance [Boy-1] of BOY

TRUE

CLIPS> (unwatch instances)

CLIPS> (reset)

CLIPS> (watch instances)

CLIPS>

(do-for-all-instances ((?b1 BOY))

(not (any-instancep ((?b2 BOY))

(> ?b2:age ?b1:age)))

(send ?b1 delete))

⇐= instance [Boy-1] of BOY

⇐= instance [Boy-2] of BOY

⇐= instance [Boy-3] of BOY

⇐= instance [Boy-4] of BOY

TRUE

CLIPS> (unwatch instances)

CLIPS>

Section 10   Defmodule Construct

CLIPS provides support for the modular development and execution of knowledge bases with the defmodule construct. CLIPS modules allow a set of constructs to be grouped together such that explicit control can be maintained over restricting the access of the constructs by other modules. This type of control is similar to global and local scoping used in languages such as C or Ada (note, however, that the global scoping used by CLIPS is strictly hierarchical and in one direction only—if module A can see constructs from module B, then it is not possible for module B to see any of module A’s constructs). By restricting access to deftemplate and defclass constructs, modules can function as blackboards, permitting only certain facts and instances to be seen by other modules. Modules are also used by rules to provide execution control.

10.1 Defining Modules

Modules are defined using the defmodule construct.

Syntax

(defmodule <module-name> [<comment>]

<port-spec>*)


<port-specification> ::= (export <port-item>) |

(import <module-name> <port-item>)

<port-item> ::= ?ALL |

?NONE |

<port-construct> ?ALL |

<port-construct> ?NONE |

<port-construct> <construct-name>+


<port-construct> ::= deftemplate | defclass |

defglobal | deffunction |

defgeneric


A defmodule cannot be redefined or even deleted once it is defined (with the exception of the MAIN module which can be redefined once). The only way to delete a module is with the clear command. Upon startup and after a clear command, CLIPS automatically constructs the following defmodule.


(defmodule MAIN)


All of the predefined system classes (see section 9.2) belong to the MAIN module. However, it is not necessary to import or export the system classes; they are always in scope. Discounting the previous exception, the predefined MAIN module does not import or export any constructs. However, unlike other modules, the MAIN module can be redefined once after startup or a clear command.


Example

(defmodule FOO

(import BAR ?ALL)

(import YAK deftemplate ?ALL)

(import GOZ defglobal x y z)

(export defgeneric +)

(export defclass ?ALL))

10.2 Specifying a Construct’s Module

The module in which a constructs is placed can be specified when the construct is defined. The deffacts, deftemplate, defrule, deffunction, defgeneric, defclass, and definstances constructs all specify the module for the construct by including it as part of the name. The module of a defglobal construct is indicated by specifying the module name after the defglobal keyword. The module of a defmessage handler is specified as part of the class specifier. The module of a defmethod is specified as part of the generic function specifier. For example, the following constructs would be placed in the DETECTION module.


(defrule DETECTION::Find-Fault

(sensor (name ?name) (value bad))

(assert (fault (name ?name))))


(defglobal DETECTION ?*count* = 0)


(defmessage-handler DETECTION::COMPONENT get-charge ()

(* ?self:flux ?self:flow))


(defmethod DETECTION::+ ((?x STRING) (?y STRING))

(str-cat ?x ?y))


Example

CLIPS> (clear)

CLIPS> (defmodule A)

CLIPS> (defmodule B)

CLIPS> (defrule foo ⇒)

CLIPS> (defrule A::bar ⇒)

CLIPS> (list-defrules)

bar

For a total of 1 defrule.

CLIPS> (set-current-module B)

A

CLIPS> (list-defrules)

foo

For a total of 1 defrule.

CLIPS>

10.3 Specifying Modules

Commands such as undefrule and ppdefrule require the name of a construct on which to operate. In previous versions of CLIPS, constructs were always referred to by their name only, so it was sufficient just to pass the name of the construct to these commands. With modules, however, it is possible to have a construct with the same name in two different modules. The modules associated with a name can be specified either explicitly or implicitly. To explicitly specify a name’s module the module name (a symbol) is listed followed by two colons, ::, and then the name is listed. The module name followed by :: is referred to as a module specifier. For example, MAIN::find stuff, refers to the find stuff construct in the MAIN module. A module can also be implicitly specified since there is always a “current” module. The current module is changed whenever a defmodule construct is defined or the set current module function is used. The MAIN module is automatically defined by CLIPS and by default is the current module when CLIPS is started or after a clear command is issued. Thus the name find stuff would implicitly have the MAIN module as its module when CLIPS is first started.


CLIPS> (clear)

CLIPS> (defmodule A)

CLIPS> (defglobal A ?*x* = 0)

CLIPS> (defmodule B)

CLIPS> (defglobal B ?*y* = 1)

CLIPS> (ppdefglobal y)

(defglobal B ?*y* = 1)

CLIPS> (ppdefglobal B::y)

(defglobal B ?*y* = 1)

CLIPS> (ppdefglobal x)

[PRNTUTIL1] Unable to find defglobal x

CLIPS> (ppdefglobal A::x)

(defglobal A ?*x* = 0)

CLIPS>

10.4 Importing and Exporting Constructs

Unless specifically exported and imported, the constructs of one module may not be used by another module. A construct is said to be visible or within scope of a module if that construct can be used by the module. For example, if module B wants to use the foo deftemplate defined in module A, then module A must export the foo deftemplate and module B must import the foo deftemplate from module A.


CLIPS> (clear)

CLIPS> (defmodule A)

CLIPS> (deftemplate A::foo (slot x))

CLIPS> (defmodule B)

CLIPS> (defrule B::bar (foo (x 3)) ⇒)


[PRNTUTIL2] Syntax Error: Check appropriate syntax for defrule


ERROR:

(defrule B::bar

(foo (

CLIPS> (clear)

CLIPS> (defmodule A (export deftemplate foo))

CLIPS> (deftemplate A::foo (slot x))

CLIPS> (defmodule B (import A deftemplate foo))

CLIPS> (defrule B::bar (foo (x 3)) ⇒)

CLIPS>


CLIPS will not allow a module or other construct to be defined that causes two constructs with the same name to be visible within the same module.

10.4.1 Exporting Constructs

The export specification in a defmodule definition is used to indicate which constructs will be accessible to other modules importing from the module being defined. Only deftemplates, defclasses, defglobals, deffunctions, and defgenerics may be exported. A module may export any valid constructs that are visible to it (not just constructs that it defines).


There are three different types of export specifications. First, a module may export all valid constructs that are visible to it. This accomplished by following the export keyword with the ?ALL keyword. Second, a module may export all valid constructs of a particular type that are visible to it. This accomplished by following the export keyword with the name of the construct type followed by the ?ALL keyword. Third, a module may export specific constructs of a particular type that are visible to it. This accomplished by following the export keyword with the name of the construct type followed by the name of one or more visible constructs of the specified type. In the following code, defmodule A exports all of its constructs; defmodule B exports all of its deftemplates; and defmodule C exports the foo, bar, and yak defglobals.


(defmodule A (export ?ALL))


(defmodule B (export deftemplate ?ALL))


(defmodule C (export defglobal foo bar yak))


The ?NONE keyword may be used in place of the ?ALL keyword to indicate either that no constructs are exported from a module or that no constructs of a particular type are exported from a module.


Defmethods and defmessage handlers cannot be explicitly exported. Exporting a defgeneric automatically exports all associated defmethods. Exporting a defclass automatically exports all associated defmessage handlers. Deffacts, definstances, and defrules cannot be exported.

10.4.2 Importing Constructs

The import specification in a defmodule definition is used to indicate which constructs the module being defined will use from other modules. Only deftemplates, defclasses, defglobals, deffunctions, and defgenerics may be imported.


There are three different types of import specifications. First, a module may import all valid constructs that are visible to a specified module. This accomplished by following the import keyword with a module name followed by the ?ALL keyword. Second, a module may import all valid constructs of a particular type that are visible to a specified module. This accomplished by following the import keyword with a module name followed by the name of the construct type followed by the ?ALL keyword. Third, a module may import specific constructs of a particular type that are visible to it. This accomplished by following the import keyword with a module name followed by the name of the construct type followed by the name of one or more visible constructs of the specified type. In the following code, defmodule A imports all of module D’s constructs; defmodule B imports all of module D’s deftemplates; and defmodule C imports the foo, bar, and yak defglobals from module D.


(defmodule A (import D ?ALL))


(defmodule B (import D deftemplate ?ALL))


(defmodule C (import D defglobal foo bar yak))


The ?NONE keyword may be used in place of the ?ALL keyword to indicate either that no constructs are imported from a module or that no constructs of a particular type are imported from a module.


Defmethods and defmessage handlers cannot be explicitly imported. Importing a defgeneric automatically imports all associated defmethods. Importing a defclass automatically imports all associated defmessage handlers. Deffacts, definstances, and defrules cannot be imported.


A module must be defined before it is used in an import specification. In addition, if specific constructs are listed in the import specification, they must already be defined in the module exporting them. It is not necessary to import a construct from the module in which it is defined in order to use it. A construct can be indirectly imported from a module that directly imports and then exports the module to be used.

10.5 Importing and Exporting Facts and Instances

Facts and instances are “owned” by the module in which their corresponding deftemplate or defclass is defined, not by the module which creates them. Facts and instances are thus visible only to those modules which import the corresponding deftemplate or defclass. This allows a knowledge base to be partitioned such that rules and other constructs can only “see” those facts and instances which are of interest to them. Note that the initial-fact deftemplate and the INITIAL OBJECT defclass must explicitly be imported from the MAIN module. Rules which have the initial-fact or initial-object pattern added to their LHS (such as a rule thats first CE is a not CE) will not be activated unless the corresponding construct for the pattern is imported.


Example

CLIPS> (clear)

CLIPS> (defmodule A (export deftemplate foo bar))

CLIPS> (deftemplate A::foo (slot x))

CLIPS> (deftemplate A::bar (slot y))

CLIPS> (deffacts A::info (foo (x 3)) (bar (y 4)))

CLIPS> (defmodule B (import A deftemplate foo))

CLIPS> (reset)

CLIPS> (facts A)

f-1 (foo (x 3))

f-2 (bar (y 4))

For a total of 2 facts.

CLIPS> (facts B)

f-1 (foo (x 3))

For a total of 1 fact.

CLIPS>

10.5.1 Specifying Instance Names

Instance names are required to be unique within a particular module, but multiple instances of the same name may be in scope at any one time. The syntax of instance names has been extended to allow module specifications (note that the left and right brackets in bold are to be typed and do not indicate an optional part of the syntax).


Syntax

<instance-name> ::= [<symbol>] |

[::<symbol>] |

[<module>::symbol>]


Specifying just a symbol as the instance name, such as [Rolls Royce], will search for the instance in the current module only. Specifying only the :: before the name, such as [::Rolls Royce], will search for the instance first in the current module and then recursively in the imported modules as defined in the module definition. Specifying both a symbol and a module name, such as [CARS::Rolls Royce], searches for the instance only in the specified module. Regardless of which format is specified, the class of the instance must be in scope of the current module in order for the instance to be found.

10.6 Modules and Rule Execution

Each module has its own pattern matching network for its rules and its own agenda. When a run command is given, the agenda of the module which is the current focus is executed (note that the reset and clear commands make the MAIN module the current focus). Rule execution continues until another module becomes the current focus, no rules are left on the agenda, or the return function is used from the RHS of a rule. Whenever a module that was focused on runs out of rules on its agenda, the current focus is removed from the focus stack and the next module on the focus stack becomes the current focus. Before a rule executes, the current module is changed to the module in which the executing rule is defined (the current focus). The current focus can be changed by using the focus command. See sections 5.2, 5.4.10.2, 12.12, and 13.12 for more details.


Example

CLIPS> (clear)

CLIPS> (defmodule MAIN (export ?ALL))

CLIPS>

(defrule MAIN::focus-example

(printout t “Firing rule in module MAIN.” crlf)

(focus A B))

CLIPS>

(defmodule A (import MAIN deftemplate initial-fact))

CLIPS>

(defrule A::example-rule

(printout t “Firing rule in module A.” crlf))

CLIPS>

(defmodule B (import MAIN deftemplate initial-fact))

CLIPS>

(defrule B::example-rule

(printout t “Firing rule in module B.” crlf))

CLIPS> (reset)

CLIPS> (run)

Firing rule in module MAIN.

Firing rule in module A.

Firing rule in module B.

CLIPS>



Section 11   Constraint Attributes

This section describes the constraint attributes that can be associated with deftemplates and defclasses so that type checking can be performed on slot values when template facts and instances are created. The constraint information is also analyzed for the patterns on the LHS of a rule to determine if the specified constraints prevent the rule from ever firing.


Two types of constraint checking are supported: static and dynamic. When static constraint checking is enabled, constraint violations are checked when function calls and constructs are parsed. This includes constraint checking between patterns on the LHS of a rule when variables are used in more than one slot. When dynamic constraint checking is enabled, newly created data objects (such as deftemplate facts and instances) have their slot values checked for constraint violations. Essentially, static constraint checking occurs when a CLIPS program is loaded and dynamic constraint checking occurs when a CLIPS program is running. By default, static constraint checking is enabled and dynamic constraint checking is disabled. The default behavior can be changed by using the set static constraint checking and set dynamic constraint checking functions.


Unless dynamic constraint checking is enabled, constraint information associated with constructs is not saved when a binary image is created using the bsave command.


The general syntax for constraint attributes is shown following.

Syntax

<constraint-attribute> ::= <type-attribute> |

<allowed-constant-attribute> |

<range-attribute> |

<cardinality-attribute>

11.1 Type Attribute

The type attribute allows the types of values to be stored in a slot to be restricted.

Syntax

<type-attribute> ::= (type <type-specification>)


<type-specification> ::= <allowed-type>+ | ?VARIABLE


<allowed-type>

::= SYMBOL | STRING | LEXEME |

INTEGER | FLOAT | NUMBER |

INSTANCE-NAME | INSTANCE-ADDRESS | INSTANCE |

EXTERNAL-ADDRESS | FACT-ADDRESS


Using NUMBER for this attribute is equivalent to using both INTEGER and FLOAT. Using LEXEME for this attribute is equivalent to using both SYMBOL and STRING. Using INSTANCE for this attribute is equivalent to using both INSTANCE NAME and INSTANCE ADDRESS. ?VARIABLE allows any type to be stored.

11.2 Allowed Constant Attributes

The allowed constant attributes allow the constant values of a specific type which can be stored in a slot to be restricted. The list of values provided should either be a list of constants of the specified type or the keyword ?VARIABLE which means any constant of that type is allowed. The allowed values attribute allows the slot to be restricted to a specific set of values (encompassing all types). Note the difference between using the attribute (allowed symbols red green blue) and (allowed values red green blue). The allowed symbols attribute states that if the value is of type symbol, then its value must be one of the listed symbols. The allowed values attribute completely restricts the allowed values to the listed values.

Syntax

<allowed-constant-attribute>

::= (allowed-symbols <symbol-list>) |

(allowed-strings <string-list>) |

(allowed-lexemes <lexeme-list> |

(allowed-integers <integer-list>) |

(allowed-floats <float-list>) |

(allowed-numbers <number-list>) |

(allowed-instance-names <instance-list>) |

(allowed-values <value-list>)


<symbol-list> ::= <symbol>+ | ?VARIABLE


<string-list> ::= <string>+ | ?VARIABLE


<lexeme-list> ::= <lexeme>+ | ?VARIABLE


<integer-list> ::= <integer>+ | ?VARIABLE


<float-list> ::= <float>+ | ?VARIABLE


<number-list> ::= <number>+ | ?VARIABLE


<instance-name-list> ::= <instance-name>+ | ?VARIABLE


<value-list> ::= <constant>+ | ?VARIABLE


Specifying the allowed lexemes attribute is equivalent to specifying constant restrictions on both symbols and strings. A string or symbol must match one of the constants in the attribute list. Type conversion from symbols to strings and strings to symbols is not performed. Similarly, specifying the allowed numbers attribute is equivalent to specifying constant restrictions on both integers and floats. In CLIPS 5.1, type conversion of integers to floats and floats to integers was performed when using the allowed numbers attribute (thus using allowed numbers was not equivalent to using both the allowed integers and allowed floats attributes together). In CLIPS 6.0, this type conversion is now longer performed. The allowed instances attribute found in CLIPS 5.1 is no longer supported. The allowed instance names attribute should be used in its place.

11.3 Range Attribute

The range attribute allows a numeric range to be specified for a slot when a numeric value is used in that slot. If a numeric value is not used in that slot, then no checking is performed.

Syntax

<range-attribute> ::= (range <range-specification>

<range-specification>)


<range-specification> ::= <number> | ?VARIABLE


Either integers or floats can be used in the range specification with the first value to the range attribute signifying the minimum allowed value and the second value signifying the maximum value. Integers will be temporarily converted to floats when necessary to perform range comparisons. If the keyword ?VARIABLE is used for the minimum value, then the minimum value is negative infinity ( ∞). If the keyword ?VARIABLE is used for the maximum value, then the maximum value is positive infinity (+∞). The range attribute cannot be used in conjunction with the allowed values, allowed numbers, allowed integers, or allowed floats attributes.

11.4 Cardinality Attribute

The cardinality attribute restricts the number of fields which can be stored in a multifield slot. This attribute can not be used with a single field slot.

Syntax

<cardinality-attribute>

::= (cardinality <cardinality-specification>

<cardinality-specification>)


<cardinality-specification> ::= <integer> | ?VARIABLE


Only integers can be used in the cardinality specification with the first value to the cardinality attribute signifying the minimum number of fields which can be stored in the slot and the second value signifying the maximum number of fields which can be stored in the slot. If the keyword ?VARIABLE is used for the minimum value, then the minimum cardinality is zero. If the keyword ?VARIABLE is used for the maximum value, then the maximum cardinality is positive infinity (+∞). If the cardinality is not specified for a multifield slot, then it is assumed to be zero to infinity.


The min number of elements and max number of elements attributes found in CLIPS 5.1 are no longer supported. The cardinality attribute should be used in their place.

11.5 Deriving a Default Value From Constraints

Default values for deftemplate and instance slots are automatically derived from the constraints for the slots if an explicit default value is not specified. The following rules are used (in order) to determine the default value for a slot with an unspecified default value.

1) The default type for the slot is chosen from the list of allowed types for the slot in the following order of precedence: SYMBOL, STRING, INTEGER, FLOAT, INSTANCE NAME, INSTANCE ADDRESS, FACT ADDRESS, EXTERNAL ADDRESS.

2) If the default type has an allowed constant restriction specified (such as the allowed-integers attribute for the INTEGER type), then the first value specified in the allowed constant attribute is chosen as the default value.


3) If the default value was not specified by step 2 and the default type is INTEGER or FLOAT and the range attribute is specified, then the minimum range value is used as the default value if it is not ?VARIABLE, otherwise, the maximum range value is used if it is not ?VARIABLE.


4) If the default value was not specified by step 2 or 3, then the default default value is used. This value is nil for type SYMBOL, ”“ for type STRING, 0 for type INTEGER, 0.0 for type FLOAT, [nil] for type INSTANCE NAME, a pointer to a dummy instance for type INSTANCE ADDRESS, a pointer to a dummy fact for type FACT ADDRESS, and the NULL pointer for type EXTERNAL ADDRESS.


5) If the default value is being derived for a single field slot, then the default value derived from steps 1 through 4 is used. The default value for a multifield slot is a multifield value of length zero. However, if the multifield slot has a minimum cardinality greater than zero, then a multifield value with a length of the minimum cardinality is created and the default value which would be used for a single field slot is stored in each field of the multifield value.

11.6 Constraint Violation Examples

The following examples illustrate some of the types of constraint violations that CLIPS can detect.

Example 1

CLIPS>

(deftemplate bar

(slot a (type SYMBOL INTEGER))

(slot b (type INTEGER FLOAT))

(slot c (type SYMBOL STRING)))

CLIPS>

(defrule error

(bar (a ?x))

(bar (b ?x))

(bar (c ?x))

⇒)


[RULECSTR1] Variable ?x in CE #3 slot c

has constraint conflicts which make the pattern unmatchable


ERROR:

(defrule error-4

(bar (a ?x))

(bar (b ?x))

(bar (c ?x))

⇒)

CLIPS>


The first occurrence of the variable ?x in slot a of the first pattern restricts its allowed types to either a symbol or integer. The second occurrence of ?x in slot b of the second pattern further restricts its allowed types to only integers. The final occurence of ?x in the third pattern generates an error because slot c expects ?x to be either a symbol of a string, but its only allowed type is an integer.

Example 2

CLIPS>

(deftemplate foo (multislot x (cardinality ?VARIABLE 3)))

CLIPS>

(deftemplate bar (multislot y (cardinality ?VARIABLE 2)))

CLIPS>

(deftemplate woz (multislot z (cardinality 7 ?VARIABLE)))

CLIPS>

(defrule error

(foo (x $?x))

(bar (y $?y))

(woz (z $?x $?y))

⇒)


[CSTRNCHK1] The group of restrictions found in CE #3

do not satisfy the cardinality restrictions for slot z


ERROR:

(defrule error

(foo (x $?x))

(bar (y $?y))

(woz (z $?x $?y))

⇒)

CLIPS>


The variable ?x, found in the first pattern, can have a maximum of two fields. The variable ?y, found in the second pattern, can have a maximum of three fields. Added together, both variables have a maximum of five fields. Since slot z in the the third pattern has a minimum cardinality of seven, the variables ?x and ?y cannot satisfy the minimum cardinality restriction for this slot.

Example 3

CLIPS> (deftemplate foo (slot x (type SYMBOL)))

CLIPS>

(defrule error

(foo (x ?x))

(test (> ?x 10))

⇒)


[RULECSTR2] Previous variable bindings of ?x caused the type restrictions for argument #1 of the expression (> ?x 10)

found in CE #2 to be violated


ERROR:

(defrule error

(foo (x ?x))

(test (> ?x 10))

⇒)

CLIPS>


The variable ?x, found in slot x of the first pattern, must be a symbol. Since the > function expects numeric values for its arguments, an error occurs.

Section 12   Actions And Functions

This section describes various actions and functions which may be used on the LHS and RHS of rules, from the top level command prompt, and from other constructs such as deffunctions, defmessage handlers, and defmethods. The terms functions, actions, and commands should be thought of interchangeably. However, when the term function is used it generally refers to a function which returns a value. The term action refers to a function having no return value but performing some basic operation as a side effect (such as printout). The term command refers to functions normally entered at the top level command prompt (such as the reset command, which does not return a value, and the set strategy command, which does return a value).

12.1 Predicate Functions

The following functions perform predicate tests.

12.1.1 Testing For Numbers

The numberp function returns the symbol TRUE if its argument is a float or integer, otherwise it returns the symbol FALSE.

Syntax

(numberp <expression>)

12.1.2 Testing For Floats

The floatp function returns the symbol TRUE if its argument is a float, otherwise it returns the symbol FALSE.

Syntax

(floatp <expression>)

12.1.3 Testing For Integers

The integerp function returns the symbol TRUE if its argument is an integer, otherwise it returns the symbol FALSE.

Syntax

(integerp <expression>)

12.1.4 Testing For Strings Or Symbols

The lexemep function returns the symbol TRUE if its argument is a string or symbol, otherwise it returns the symbol FALSE.

Syntax

(lexemep <expression>)

12.1.5 Testing For Strings

The stringp function returns the symbol TRUE if its argument is a string, otherwise it returns the symbol FALSE.

Syntax

(stringp <expression>)

12.1.6 Testing For Symbols

The symbolp function returns the symbol TRUE if its argument is a symbol, otherwise it returns the symbol FALSE. This function may also be called using the name wordp.

Syntax

(symbolp <expression>)

12.1.7 Testing For Even Numbers

The evenp function returns the symbol TRUE if its argument is an even number, otherwise it returns the symbol FALSE.

Syntax

(evenp <integer-expression>)

12.1.8 Testing For Odd Numbers

The oddp function returns the symbol TRUE if its argument is an odd number, otherwise it returns the symbol FALSE.

Syntax

(oddp <integer-expression>)

12.1.9 Testing For Multifield Values

The multifieldp function returns the symbol TRUE if its argument is a multifield value, otherwise it returns the symbol FALSE. This function may also be called using the name sequencep.

Syntax

(multifieldp <expression>)

12.1.10 Testing For External Addresses

The pointerp function returns the symbol TRUE if its argument is an external address, otherwise it returns the symbol FALSE. External address;es are discussed in further detail in the Advanced Programming Guide.

Syntax

(pointerp <expression>)

12.1.11 Comparing for Equality

The eq function returns the symbol TRUE if its first argument is equal in value to all its subsequent arguments, otherwise it returns the symbol FALSE. Note that eq compares types as well as values. Thus, (eq 3 3.0) is FALSE since 3 is an integer and 3.0 is a float.

Syntax

(eq <expression> <expression>+)

Example

CLIPS> (eq foo bar mumble foo)

FALSE

CLIPS> (eq foo foo foo foo)

TRUE

CLIPS> (eq 3 4)

FALSE

CLIPS>

12.1.12 Comparing for Inequality

The neq function returns the symbol TRUE if its first argument is not equal in value to all its subsequent arguments, otherwise it returns the symbol FALSE. Note that neq compares types as well as values. Thus, (neq 3 3.0) is TRUE since 3 is an integer and 3.0 is a float.

Syntax

(neq <expression> <expression>+)

Example

CLIPS> (neq foo bar yak bar)

TRUE

CLIPS> (neq foo foo yak bar)

FALSE

CLIPS> (neq 3 a)

TRUE

CLIPS>

12.1.13 Comparing Numbers for Equality

The = function returns the symbol TRUE if its first argument is equal in value to all its subsequent arguments, otherwise it returns the symbol FALSE. Note that = compares only numeric values and will convert integers to floats when necessary for comparison.

Syntax

(= <numeric-expression> <numeric-expression>+)

Example

CLIPS> (= 3 3.0)

TRUE

CLIPS> (= 4 4.1)

FALSE

CLIPS>

Portability Note

Because the precision of floating point numbers varies from one machine to another, it is possible for the numeric comparison functions to work correctly one machine and incorrectly on another. In fact, you should be aware, even if code is not being ported, that roundoff error can cause erroneous results. For example, the following expression erroneously returns the symbol TRUE because both numbers are rounded up to 0.6666666666666666667.


CLIPS> (= 0.66666666666666666666 0.66666666666666666667)

TRUE

CLIPS>

12.1.14 Comparing Numbers for Inequality

The <> function returns the symbol TRUE if its first argument is not equal in value to all its subsequent arguments, otherwise it returns the symbol FALSE. Note that <> compares only numeric values and will convert integers to floats when necessary for comparison.

Syntax

(<> <numeric-expression> <numeric-expression>+)

Example

CLIPS> (<> 3 3.0)

FALSE

CLIPS> (<> 4 4.1)

TRUE

CLIPS>

Portability Note

See portability note in section 12.1.13.

12.1.15 Greater Than Comparison

The > function returns the symbol TRUE if for all its arguments, argument n 1 is greater than argument n, otherwise it returns the symbol FALSE. Note that > compares only numeric values and will convert integers to floats when necessary for comparison.

Syntax

(> <numeric-expression> <numeric-expression>+)

Example

CLIPS> (> 5 4 3)

TRUE

CLIPS> (> 5 3 4)

FALSE

CLIPS>

Portability Note

See portability note in section 12.1.13.

12.1.16 Greater Than or Equal Comparison

The >= function returns the symbol TRUE if for all its arguments, argument n 1 is greater than or equal to argument n, otherwise it returns the symbol FALSE. Note that >= compares only numeric values and will convert integers to floats when necessary for comparison.

Syntax

(>= <numeric-expression> <numeric-expression>+)

Example

CLIPS> (>= 5 5 3)

TRUE

CLIPS> (>= 5 3 5)

FALSE

CLIPS>

Portability Note

See portability note in section 12.1.13.

12.1.17 Less Than Comparison

The < function returns the symbol TRUE if for all its arguments, argument n 1 is less than argument n, otherwise it returns the symbol FALSE. Note that < compares only numeric values and will convert integers to floats when necessary for comparison.

Syntax

(< <numeric-expression> <numeric-expression>+)

Example

CLIPS> (< 3 4 5)

TRUE

CLIPS> (< 3 5 4)

FALSE

CLIPS>

Portability Note

See portability note in section 12.1.13.

12.1.18 Less Than or Equal Comparison

The function returns the symbol TRUE if for all its arguments, argument n 1 is less than or equal to argument n, otherwise it returns the symbol FALSE. Note that compares only numeric values and will convert integers to floats when necessary for comparison.

Syntax

(⇐ <numeric-expression> <numeric-expression>+)

Example

CLIPS> (⇐ 3 5 5)

TRUE

CLIPS> (⇐ 5 3 5)

FALSE

CLIPS>

Portability Note

See portability note in section 12.1.13.

12.1.19 Boolean And

The and function returns the symbol TRUE if each of its arguments evaluates to TRUE, otherwise it returns the symbol FALSE. The and function performs short circuited boolean logic. Each argument of the function is evaluated from left to right. If any argument evaluates to FALSE, then the symbol FALSE is immediately returned by the function.

Syntax

(and <expression>+)

12.1.20 Boolean Or

The or function returns the symbol TRUE if any of its arguments evaluates to TRUE, otherwise it returns the symbol FALSE. The or function performs short circuited boolean logic. Each argument of the function is evaluated from left to right. If any argument evaluates to TRUE, then the symbol TRUE is immediately returned by the function.

Syntax

(or <expression>+)

12.1.21 Boolean Not

The not function returns the symbol TRUE if its argument evaluates to FALSE, otherwise it returns the symbol FALSE.

Syntax

(not <expression>)

12.2 Multifield Functions

The following functions operate on multifield values.

12.2.1 Creating Multifield Values

This function appends any number of fields together to create a multifield value.

Syntax

(create$ <expression>*)


The return value of create$ is a multifield value regardless of the number or types of arguments (single field or multifield). Calling create$ with no arguments creates a multifield value of length zero.

Example

CLIPS (create$ hammer drill saw screw pliers wrench)

(hammer drill saw screw pliers wrench)

CLIPS> (create$ (+ 3 4) (* 2 3) (/ 8 4))

(7 6 2)

CLIPS>

12.2.2 Specifying an Element

The nth$ function will return a specified field from a multifield value.

Syntax

(nth$ <integer-expression> <multifield-expression>)


where the first argument should be an integer from 1 to the number of elements within the second argument. The symbol nil will be returned if the first argument is greater than the number of fields in the second argument.

Example

CLIPS> (nth$ 3 (create$ a b c d e f g))

c

CLIPS>

12.2.3 Finding an Element

The member$ function will tell if a single field value is contained in a multifield value.

Syntax

(member$ <expression> <multifield-expression>)


If the first argument is a single field value and is one of the fields within the second argument, member$ will return the integer position of the field (from 1 to the length of the second argument). If the first argument is a multifield value and this value is embedded in the second argument, then the return value is a two field multifield value consisting of the starting and ending integer indices of the first argument within the second argument. If neither of these situations is satisfied, then FALSE is returned.

Example

CLIPS> (member$ blue (create$ red 3 “text” 8.7 blue))

5

CLIPS> (member$ 4 (create$ red 3 “text” 8.7 blue))

FALSE

CLIPS> (member$ (create$ b c) (create$ a b c d))

(2 3)

CLIPS>

12.2.4 Comparing Multifield Values

This function checks if one multifield value is a subset of another; i.e., if all the fields in the first multifield value are also in the second multifield value.

Syntax

(subsetp <multifield-expression> <multifield-expression>)


If the first argument is a subset of the second argument, the function returns TRUE; otherwise, it returns FALSE. The order of the fields is not consi­dered. If the first argument is bound to a multifield of length zero, the subsetp function always returns TRUE.

Example

CLIPS> (subsetp (create$ hammer saw drill)

(create$ hammer drill wrench pliers saw))

TRUE

CLIPS> (subsetp (create$ wrench crowbar)

(create$ hammer drill wrench pliers saw))

FALSE

CLIPS>

12.2.5 Deletion of Fields in Multifield Values

This function deletes the specified range from a multifield value.

Syntax

(delete$ <multifield-expression>

<begin-integer-expression>

<end-integer-expression>)


The modified multifield value is returned, which is the same as <multifield expression> with the fields ranging from <begin integer expression> to <end integer expression> removed. To delete a single field, the begin range field should equal the end range field.

Example

CLIPS> (delete$ (create$ hammer drill saw pliers wrench) 3 4)

(hammer drill wrench)

CLIPS> (delete$ (create$ computer printer hard-disk) 1 1)

(printer hard-disk)

CLIPS>

12.2.6 Creating Multifield Values from Strings.

This function constructs a multifield value from a string by using each field in a string as a field in a new multifield value.

Syntax

(explode$ <string-expression>)


A new multifield value is created in which each delimited field in order in <string expression> is taken to be a field in the new multifield value which is returned. A string with no fields creates a multifield value of length zero. Fields other than symbols, strings, integer, floats, or instances names (such as parentheses or variables) are converted to strings.

Example


CLIPS> (explode$ “hammer drill saw screw”)

(hammer drill saw screw)

CLIPS> (explode$ “1 2 abc 3 4 \”abc\” \“def\”“)

(1 2 abc 3 4 “abc” “def”)

CLIPS> (explode$ ”?x ~ )“)

(”?x“ ”~“ ”)“)

CLIPS>

12.2.7 Creating Strings from Multifield Values

This function creates a single string from a multifield value.

Syntax

(implode$ <multifield-expression>)


Each field in <multifield expression> in order is concatenated into a string value with a single blank sepa­rating fields. The new string is returned.

Example

CLIPS> (implode$ (create$ hammer drill screwdriver))

“hammer drill screwdriver wrench pliers saw”

CLIPS> (implode$ (create$ 1 “abc” def “ghi” 2))

“1 “abc” def “ghi” 2”

CLIPS> (implode$ (create$ “abc def ghi”))

”“abc def ghi”“

CLIPS>

12.2.8 Extracting a Sub sequence from a Multifield Value

This function extracts a specified range from a multifield value and returns a new mul­tifield value containing just the sub sequence.

Syntax

(subseq$ <multifield-value>

<begin-integer-expression>

<end-integer-expression>)


where the second and third arguments are integers specifying the begin and end fields of the desired sub sequence in <multifield expression>.

Example

CLIPS> (subseq$ (create$ hammer drill wrench pliers) 3 4)

(wrench pliers)

CLIPS> (subseq$ (create$ 1 “abc” def “ghi” 2) 1 1)

(1)

CLIPS>

12.2.9 Replacing Fields within a Multifield Value

This function replaces a range of field in a multifield value with a series of single field and/or multifield values and returns a new mul­tifield value containing the replacement values within the original multifield value.

Syntax

(replace$ <multifield-expression>

<begin-integer-expression>

<end-integer-expression>

<single-or-multi-field-expression>+)


where <begin integer expression> to <end integer expression> is the range of values to be replaced.

Example

CLIPS> (replace$ (create$ drill wrench pliers) 3 3 machete)

(drill wrench machete)

CLIPS> (replace$ (create$ a b c d) 2 3 x y (create$ q r s))

(a x y q r s d)

CLIPS>

12.2.10 Inserting Fields within a Multifield Value

This function inserts a series of single field and/or multifield values at a specified location in a multifield value with and returns a new mul­tifield value containing the inserted values within the original multifield value.

Syntax

(insert$ <multifield-expression>

<integer-expression>

<single-or-multi-field-expression>+)


where <integer expression> is the location where the values are to be inserted. This value must be greater than or equal to 1. A value of 1 inserts the new value(s) at the beginning of the <multifield expression>. Any value greater than the length of the <multifield expression> appends the new values to the end of the <multifield expression>.

Example

CLIPS> (insert$ (create$ a b c d) 1 x)

(x a b c d)

CLIPS> (insert$ (create$ a b c d) 4 y z)

(a b c y z d)

CLIPS> (insert$ (create$ a b c d) 5 (create$ q r))

(a b c d q r)

CLIPS>


12.2.11 Getting the First Field from a Multifield Value

This function returns the first field of a multifield value as a multifield value

Syntax

(first$ <multifield-expression>)

Example

CLIPS> (first$ (create$ a b c))

(a)

CLIPS> (first$ (create$))

()

CLIPS>

12.2.12 Getting All but the First Field from a Multifield Value

This function returns all but the first field of a multifield value as a multifield value.

Syntax

(rest$ <multifield-expression>)

Example

CLIPS> (rest$ (create$ a b c))

(b c)

CLIPS> (rest$ (create$))

()

CLIPS>

12.2.13 Determining the Number of Fields in a Multifield Value

The length$ function returns an integer indicating the number of fields contained in a multifield value. If the argument passed to length$ is not the appropriate type, a negative one ( 1) is returned.

Syntax

(length$ <multifield-expression>)

Example

CLIPS> (length$ (create$ a b c d e f g))

7

CLIPS>

12.2.14 Deleting Specific Values within a Multifield Value

This function deletes specific values contained within a multifield value and returns the modified multifield value.

Syntax

(delete-member$ <multifield-expression> <expression>+)


where <expression>+ is one or more values to be deleted from <multifield-expression>. If <expression> is a multifield value, the entire sequence must be contained within the first argument in the correct order.

Example

CLIPS> (delete-member$ (create$ a b a c) b a)

©

CLIPS> (delete-member$ (create$ a b c c b a) (create$ b a))

(a b c c)

CLIPS>

12.2.15 Replacing Specific Values within a Multifield Value

This function replaces specific values contained within a multifield value and returns the modified multifield value.

Syntax

(replace-member$ <multifield-expression> <substitute-expression>

<search-expression>+)


where any <search-expression> that is contained within <multifield-expression> is replaced by <substitute-expression>.

Example

CLIPS> (replace-member$ (create$ a b a b) (create$ a b a) a b)

(a b a a b a a b a a b a)

CLIPS> (replace-member$ (create$ a b a b) (create$ a b a) (create$ a b))

(a b a a b a)

CLIPS>

12.3 String Functions

The following functions perform operations that are related to strings.

12.3.1 String Concatenation

The str cat function will concatenates its arguments into a single string.

Syntax

(str-cat <expression>*)


Each <expression> should be one of the following types: symbol, string, float, integer, or instance name.

Example

CLIPS> (str-cat “foo” bar)

“foobar”

CLIPS>

12.3.2 Symbol Concatenation

The sym cat function will concatenate its arguments into a single symbol. It is functionally identical to the str cat function with the exception that the returned value is a symbol and not a string.

Syntax

(sym-cat <expression>*)


Each <expression> should be one of the following types: symbol, string, float, integer, or instance name.

12.3.3 Taking a String Apart

The sub string function will retrieve a portion of a string from another string.

Syntax

(sub-string <integer-expression> <integer-expression>

<string-expression>)


where the first argument, counting from one, must be a number marking the begin­ning position in the string and the second argument must be a number marking the ending position in the string. If the first argument is greater than the second argument, a null string is returned.

Example

CLIPS> (sub-string 3 8 “abcdefghijkl”)

“cdefgh”

CLIPS>

12.3.4 Searching a String

The str index function will return the position of a string inside another string.

Syntax

(str-index <lexeme-expression> <lexeme-expression>)


where the second argument is searched for the first occurrence of the first argument. The str index function re­turns the integer starting position, counting from one, of the first argument in the second argument or returns the symbol FALSE if not found.

Example

CLIPS> (str-index “def” “abcdefghi”)

4

CLIPS> (str-index “qwerty” “qwertypoiuyt”)

1

CLIPS> (str-index “qwerty” “poiuytqwer”)

FALSE

CLIPS>

12.3.5 Evaluating a Function within a String

The eval function evaluates the string as though it were entered at the command prompt.

Syntax

(eval <string-or-symbol-expression>)


where the only argument is the command, constant, or global variable to be executed. NOTE: eval does not permit the use of local variables (except when the local variables are defined as part of the command such as with an instance query function), nor will it evaluate any of the construct definition forms (i.e., defrule, deffacts, etc.;). The return value is the result of the evaluation of the string (or FALSE if an error occurs).


The eval function is not available for binary-load only or run time CLIPS configurations (see the Advanced Programming Guide).

Example

CLIPS> (eval ”(+ 3 4)“)

7

CLIPS> (eval ”(create$ a b c)“)

(a b c)

CLIPS>

12.3.6 Evaluating a Construct within a String

The build function evaluates the string as though it were entered at the command prompt.

Syntax

(build <string-or-symbol-expression>)


where the only argument is the construct to be added. The return value is TRUE if the construct was added (or FALSE if an error occurs).


The build function is not available for binary-load only or run time CLIPS configurations (see the Advanced Programming Guide).

Example

CLIPS> (clear)

CLIPS> (build ”(defrule foo (a) ⇒ (assert (b)))“)

TRUE

CLIPS> (rules)

foo

For a total of 1 rule.

CLIPS>

12.3.7 Converting a String to Uppercase

The upcase function will return a string or symbol with uppercase alphabetic characters.

Syntax

(upcase <string-or-symbol-expression>)

Example

CLIPS> (upcase “This is a test of upcase”)

“THIS IS A TEST OF UPCASE”

CLIPS> (upcase A_Word_Test_for_Upcase)

A_WORD_TEST_FOR_UPCASE

CLIPS>

12.3.8 Converting a String to Lowercase

The lowcase function will return a string or symbol with lowercase alphabetic characters.

Syntax

(lowcase <string-or-symbol-expression>)

Example

CLIPS> (lowcase “This is a test of lowcase”)

“this is a test of lowcase”

CLIPS> (lowcase A_Word_Test_for_Lowcase)

a_word_test_for_lowcase

CLIPS>

12.3.9 Comparing Two Strings

The str compare function will compare two strings to determine their logical relationship (i.e., equal to, less than, greater than). The comparison is performed character by character until the strings are exhausted (implying equal strings) or un­equal characters are found. The positions of the unequal characters within the ASCII character set are used to determine the logical relationship of unequal strings.

Syntax

(str-compare <string-or-symbol-expression>

<string-or-symbol-expression>)


This function returns an integer representing the result of the comparison (0 if the strings are equal, < 0 if the first argument < the second argument, and > 0 if the first argument > the second argument).

Example

CLIPS> (< (str-compare “string1” “string2”) 0)

TRUE ; since “1” < “2” in ASCII character set

CLIPS> (str-compare “abcd” “abcd”)

0

CLIPS>

12.3.10 Determining the Length of a String

The str length function returns the length of a string as an integer.

Syntax

(str-length <string-or-symbol-expression>)

Example

CLIPS> (str-length “abcd”)

4

CLIPS> (str-length xyz)

3

CLIPS>

12.3.11 Checking the Syntax of a Construct or Function Call within a String

The function check-syntax allows the text representation of a construct or function call to be checked for syntax and semantic errors.

Syntax

(check-syntax <construct-or-function-string>)


This function returns FALSE if there are no errors or warnings encountered parsing the construct or function call. The symbol MISSING-LEFT-PARENTHESIS is returned if the first token is not a left parenthesis. The symbol EXTRANEOUS-INPUT-AFTER-LAST-PARENTHESIS is returned if there are additional tokens after the closing right parenthesis of the construct or function call. If errors or warnings are encounted parsing, the a multifield of length two is returned. The first field of the multifield is a string containing the text of the error message (or the symbol FALSE if no errors were encountered). The second field of the multifield is a string containing the text of the warning message (or the symbol FALSE if no warnings were encountered).

Example

CLIPS> (check-syntax ”(defrule example ⇒)“)

FALSE

CLIPS> (check-syntax ”(defrule foo (number 40000000000000) ⇒)“)

(FALSE ”[SCANNER1] WARNING: Over or underflow of long integer.

“)

CLIPS> (check-syntax ”(defrule example (3) ⇒)“)

(”

[PRNTUTIL2] Syntax Error: Check appropriate syntax for the first field of a pattern.


ERROR:

(defrule MAIN::example

(3

“ FALSE)

CLIPS>

12.3.12 Converting a String to a Field

The string-to-field function parses a string and converts its contents to a primitive data type.

Syntax

(string-to-field <string-or-symbol-expression>)


where the only argument is the string to be parsed. Essentially calling string-to-field with its string argument is equivalent to calling the read function and manually typing the contents of the string argument or reading it from a file. It is preferable to call string-to-field rather than eval to convert a string to a primitive data type since the eval function is not available for binary-load only or run-time CLIPS configurations (see the Advanced Programming Guide).

Example

CLIPS> (string-to-field “3.4”)

3.4

CLIPS> (string-to-field “a b”)

a

CLIPS>

12.4 The CLIPS I/O System

CLIPS uses a system called I/O routers to provide very flexible I/O while remaining portable. A more complete discussion of I/O routers is covered in the Advanced Programming Guide.

12.4.1 Logical Names

One of the key concepts of I/O routing is the use of logical names. Logical names allow reference to an I/O device without having to understand the details of the imple­mentation of the reference. Many functions in CLIPS make use of logical names. A logical name can be either a symbol, a number, or a string. Several logical names are predefined by CLIPS and are used extensively throughout the CLIPS code. These are


* Name Description stdin The default for all user inputs. The read and readline functions read from stdin if t is specified as the logical name. stdout The default for all user outputs. The format and printout functions send output to stdout if t is specified as the logical name. wclips The CLIPS prompt is sent to this logical name. wdialog All informational messages are sent to this logical name. wdisplay Requests to display CLIPS information, such as facts or rules, are sent to this logical name. werror All error messages are sent to this logical name. wwarning All warning messages are sent to this logical name. wtrace All watch information is sent to this logical name (with the exception of compilations which is sent to wdialog).


Any of these logical names may be used anywhere a logical name is expected.

12.4.2 Common I/O Functions

CLIPS provides some of the most commonly needed I/O capabilities through several predefined functions.

12.4.2.1 Open

The open function allows a user to open a file from the RHS of a rule and attaches a logical name to it. This function takes three arguments: (1) the name of the file to be opened; (2) the logical name which will be used by other CLIPS I/O functions to ac­cess the file; and (3) an optional mode specifier. The mode specifier must be one of the fol­lowing strings:


* Mode Means “r” read access only “w” write access only “r+“ read and write access “a” append access only “wb” binary write access


If the mode is not specified, a default of read access only is assumed. The access mode may not be meaningful in some operating systems.

Syntax

(open <file-name> <logical-name> [<mode>])


The <file name> must either be a string or symbol and may include directory speci­fiers. If a string is used, the backslash (\) and any other special characters that are part of <file name> must be escaped with a backslash. The logical name should not have been used previously. The open function returns TRUE if it was successful, otherwise FALSE.

Example

CLIPS> (open “myfile.clp” writeFile “w”)

TRUE

CLIPS> (open “MS-DOS\\directory\\file.clp” readFile)

TRUE

CLIPS>

12.4.2.2 Close

The close function closes a file stream previously opened with the open com­mand. The file is specified by a logical name previously attached to the desired stream.

Syntax

(close [<logical-name>])


If close is called without arguments, all open files will be closed. The user is responsible for closing all files opened during execution. If files are not closed, the contents are not guaranteed correct, however, CLIPS will attempt to close all open files when the exit command is executed. The close function returns TRUE if any files were successfully closed, otherwise FALSE.

Example

CLIPS> (open “myfile.clp” writeFile “w”)

TRUE

CLIPS> (open “MS-DOS\\directory\\file.clp” readFile)

TRUE

CLIPS> (close writeFile)

TRUE

CLIPS> (close writeFile)

FALSE

CLIPS> (close)

TRUE

CLIPS> (close)

FALSE

CLIPS>

12.4.2.3 Printout

The function printout allows output to a device attached to a logical name. The logical name must be specified and the device must have been prepared previously for output (e.g., a file must be opened first). To send output to stdout, use a t for the logical name. If the logical name nil is used, the printout function does nothing.

Syntax

(printout <logical-name> <expression>*)


Any number of expressions may be placed in a printout to be printed. Each expression is evaluated and printed (with no spaces added between each printed expression). The symbol crlf used as an <expression> will force a carriage return/newline and may be placed anywhere in the list of expressions to be printed. Similarly, the symbols tab, vtab, and ff will print respectively a tab, a vertical tab, and a form feed. The appearance of these special symbols may vary from one operating system to another. The printout function strips quotation marks from around strings when it prints them. Fact addresses, instance addresses and external addresses can be printed by the printout function. This function has no return value.

Example

CLIPS> (printout t “Hello there!” crlf)

Hello There!

CLIPS> (open “data.txt” mydata “w”)

TRUE

CLIPS> (printout mydata “red green”)

CLIPS> (close)

TRUE

CLIPS>

12.4.2.4 Read

The read function allows a user to input information for a single field. All of the stan­dard field rules (e.g., multiple symbols must be embedded within quotes) apply.

Syntax

(read [<logical-name>])


where <logical name> is an optional parameter. If specified, read tries to read from whatever is attached to the logical file name. If <logical name> is t or is not speci­fied, the function will read from stdin. All the delimiters defined in section 2.3.1 can be used as delimiters. The read function always returns a primitive data type. Spaces, carriage returns, and tabs only act as delimiters and are not contained within the return value (unless these characters are included within double quotes as part of a string). If an end of file (EOF) is encountered while reading, read will return the symbol EOF. If errors are encountered while reading, the string ”*** READ ERROR ***” will be returned.

Example

CLIPS> (open “data.txt” mydata “w”)

TRUE

CLIPS> (printout mydata “red green”)

CLIPS> (close)

TRUE

CLIPS> (open “data.txt” mydata)

TRUE

CLIPS> (read mydata)

red

CLIPS> (read mydata)

green

CLIPS> (read mydata)

EOF

CLIPS> (close)

TRUE

CLIPS>

12.4.2.5 Readline

The readline function is similar to the read function, but it allows a whole string to be input instead of a single field. Normally, read will stop when it encounters a delimiter. The readline function only stops when it encounters a carriage return, a semicolon, or an EOF. Any tabs or spaces in the input are returned by readline as a part of the string. The readline function returns a string.

Syntax

(readline [<logical-name>])


where <logical name> is an optional parameter. If specified, readline tries to read from whatever is attached to the logical file name. If <logical name> is t or is not spec­i­fied, the function will read from stdin. As with the read function, if an EOF is encountered, readline will return the symbol EOF. If an error is encountered during input, readline returns the string ”*** READ ERROR ***“.

Example

CLIPS> (open “data.txt” mydata “w”)

TRUE

CLIPS> (printout mydata “red green”)

CLIPS> (close)

TRUE

CLIPS> (open “data.txt” mydata)

TRUE

CLIPS> (readline mydata)

“red green”

CLIPS> (readline mydata)

EOF

CLIPS> (close)

TRUE

CLIPS>

12.4.2.6 Format

The format function allows a user to send formatted output to a device attached to a logical name. It can be used in place of printout when special formatting of out­put information is desired. Although a slightly more complicated function, format pro­vides much better control over how the output is formatted. The format commands are simi­lar to the printf statement in C. The format function always returns a string containing the formatted output. A logical name of nil may be used when the formatted return string is desired without writing to a device.

Syntax

(format <logical-name> <string-expression> <expression>*)


If tis given, output is sent to stdout. The second argument to format, called the control string, specifies how the output should be formatted. Subsequent arguments to format (the parameter list for the control string) are the expressions which are to be out­put as indicated by the control string. Format currently does not allow expressions returning multifield values to be included in the parameter list.


The control string consists of text and format flags. Text is output exactly as speci­fied, and format flags describe how each parameter in the parameter list is to be for­matted. The first format flag corresponds to the first value in the parameter list, the second flag corresponds to the second value, etc. The format flags must be preceded by a percent sign (%) and are of the general format


% M.Nx


where x is one of the flags listed below, the minus sign is an optional justification flag, and M and N are optional parameters which specify the field width and number of dig­its following the decimal place. If M is used, at least M characters will be output. If more than M characters are required to display the value, format expands the field as needed. If M starts with a 0 (e.g., %07d), a zero is used as the pad character; oth­er­wise, spaces are used. If N is not specified, it defaults to six digits for floating point numbers. If a minus sign is included before the M, the value will be left justified; oth­erwise the value is right justified.



* Format Flag
Meaning c Display parameter as single character. d Display parameter as a long integer. (The N specifier has no meaning.)

f Display parameter as a floating point number.

e Display parameter as a floating point using power of 10 notation.

g Display parameter in the most general format, whichever is shorter.

o Display parameter as an unsigned octal number. (The N specifier has no meaning.)

x Display parameter as an unsigned hexadecimal number. (The N specifier has no meaning.)

s Display parameter as a string. Strings will have the leading and trailing quotes stripped. (The N specifier indicates the maximum number of characters to be printed. Zero also cannot be used for the pad character.)

n Put a new line in the output.

r Put a carriage return in the output.

% Put the percent character into the output.

Example

CLIPS> (format t “Hello World!%n”)

Hello World!

“Hello World!

CLIPS> (format nil “Integer: |%ld|” 12)

“Integer: |12|”

CLIPS> (format nil “Integer: |%4ld|” 12)

“Integer: | 12|”

CLIPS> (format nil “Integer: |%-04ld|” 12)

“Integer: |12 |”

CLIPS> (format nil “Float: |%f|” 12.01)

“Float: |12.010000|”

CLIPS> (format nil “Float: |%7.2f| “12.01)

“Float: | 12.01| ”

CLIPS> (format nil “Test: |%e|” 12.01)

“Test: |1.201000e+01|”

CLIPS> (format nil “Test: |%7.2e|” 12.01)

“Test: |1.20e+01|”

CLIPS> (format nil “General: |%g|” 1234567890)

“General: |1.23457e+09|”

CLIPS> (format nil “Hexadecimal: |%x|” 12)

“Hexadecimal: |c|”

CLIPS> (format nil “Octal: |%o|” 12)

“Octal: |14|”

CLIPS> (format nil “Symbols: |%s| |%s|” value-a1 capacity)

“Symbols: |value-a1| |capacity|”

CLIPS>

Portability Note

The format function uses the C function sprintf as a base. Some systems may not support sprintf or may not support all of these features, which may affect how format works.

12.4.2.7 Rename

The rename function is used to change the name of a file.

Syntax

(rename <old-file-name> <new-file-name>)


Both <old file name> and <new file name> must either be a string or symbol and may include directory speci­fiers. If a string is used, the backslash (\) and any other special characters that are part of either <old file name> or <new file name> must be escaped with a backslash. The rename function returns TRUE if it was successful, otherwise FALSE.


Portability Note

The rename function uses the ANSI C function rename as a base. If the ANSI_COMPILER flag was disabled when CLIPS was compiled, then this function will be non functional and always return FALSE.

12.4.2.8 Remove

The remove function is used to delete a file.

Syntax

(remove <file-name>)


The <file name> must either be a string or symbol and may include directory speci­fiers. If a string is used, the backslash (\) and any other special characters that are part of <file name> must be escaped with a backslash. The remove function returns TRUE if it was successful, otherwise FALSE.


Portability Note

The remove function uses the ANSI C function remove as a base. If the ANSI_COMPILER flag was disabled when CLIPS was compiled, then this function will be non functional and always return FALSE.

12.5 Math Functions

CLIPS provides several functions for mathematical computa­tions. They are split into two packages: a set of standard math functions and a set of extended math functions.

12.5.1 Standard Math Functions

The standard math functions are listed below. These func­tions should be used only on numeric arguments. An error message will be printed if a string argument is passed to a math function.

12.5.1.1 Addition

The + function returns the sum of its arguments. Each of its arguments should be a numeric expression. Addition is performed using the type of the arguments provided unless mixed mode arguments (integer and float) are used. In this case, the function return value and integer arguments are converted to floats after the first float argument has been encountered. This function returns a float if any of its arguments is a float, otherwise it returns an integer.

Syntax

(+ <numeric-expression> <numeric-expression>+)

Example

CLIPS> (+ 2 3 4)

9

CLIPS> (+ 2 3.0 5)

10.0

CLIPS> (+ 3.1 4.7)

7.8

CLIPS>

12.5.1.2 Subtraction

The   function returns the value of the first argument minus the sum of all subsequent arguments. Each of its arguments should be a numeric expression. Subtraction is performed using the type of the arguments provided unless mixed mode arguments (integer and float) are used. In this case, the function return value and integer arguments are converted to floats after the first float argument has been encountered. This function returns a float if any of its arguments is a float, otherwise it returns an integer.

Syntax

(- <numeric-expression> <numeric-expression>+)

Example

CLIPS> (- 12 3 4)

5

CLIPS> (- 12 3.0 5)

4.0

CLIPS> (- 4.7 3.1)

1.6

CLIPS>

12.5.1.3 Multiplication

The * function returns the product of its arguments. Each of its arguments should be a numeric expression. Multiplication is performed using the type of the arguments provided unless mixed mode arguments (integer and float) are used. In this case, the function return value and integer arguments are converted to floats after the first float argument has been encountered. This function returns a float if any of its arguments is a float, otherwise it returns an integer.

Syntax

(* <numeric-expression> <numeric-expression>+)

Example

CLIPS> (* 2 3 4)

24

CLIPS> (* 2 3.0 5)

30.0

CLIPS> (* 3.1 4.7)

14.57

CLIPS>

12.5.1.4 Division

The / function returns the value of the first argument divided by each of the subsequent arguments. Each of its arguments should be a numeric expression. Division is performed using the type of the arguments provided unless mixed mode arguments (integer and float) are used. In this case, the function return value and integer arguments are converted to floats after the first float argument has been encountered. By default, the dividend (the first argument) is automatically converted to a floating point number so that the result is a floating pointer number. The function set auto float dividend can be used to control this behavior. If for example, the auto float feature is disabled, the expression (/ 4 3 4.0) evaluates to 0.25 as opposed to 0.333333333 if this feature were enabled. This function returns a float if any of its arguments is a float, otherwise it returns an integer.

Syntax

(/ <numeric-expression> <numeric-expression>+)

Example

CLIPS> (/ 4 2)

2.0

CLIPS> (/ 4.0 2.0)

2.0

CLIPS> (/ 24 3 4)

2.0

CLIPS>

12.5.1.5 Integer Division

The div function returns the value of the first argument divided by each of the subsequent arguments. Each of its arguments should be a numeric expression. Each argument is automatically converted to an integer and integer division is performed. This function returns an integer.

Syntax

(div <numeric-expression> <numeric-expression>+)

Example

CLIPS> (div 4 2)

2

CLIPS> (div 5 2)

2

CLIPS> (div 33 2 3 5)

1

CLIPS>

12.5.1.6 Maximum Numeric Value

The max function returns the value of its largest numeric argument. Each of its arguments should be a numeric expression. When necessary, integers are temporarily converted to floats for comparison. The return value will either be integer or float (depending upon the type of the largest argument).

Syntax

(max <numeric-expression>+)

Example

CLIPS> (max 3.0 4 2.0)

4

CLIPS>

12.5.1.7 Minimum Numeric Value

The min function returns the value of its smallest numeric argument. Each of its arguments should be a numeric expression. When necessary, integers are temporarily converted to floats for comparison. The return value will either be integer or float (depending upon the type of the smallest argument).

Syntax

(min <numeric-expression>+)

Example

CLIPS> (min 4 0.1 -2.3)

-2.3

CLIPS>

12.5.1.8 Absolute Value

The abs function returns the absolute value of its only argument (which should be a numeric expression). The return value will either be integer or float (depending upon the type the argument).

Syntax

(abs <numeric-expression>)

Example

CLIPS> (abs 4.0)

4.0

CLIPS> (abs -2)

2

CLIPS>

12.5.1.9 Convert To Float

The float function converts its only argument (which should be a numeric expression) to type float and returns this value.

Syntax

(float <numeric-expression>)

Example

CLIPS> (float 4.0)

4.0

CLIPS> (float -2)

-2.0

CLIPS>

12.5.1.10 Convert To Integer

The integer function converts its only argument (which should be a numeric expression) to type integer and returns this value.

Syntax

(integer <numeric-expression>)

Example

CLIPS> (integer 4.0)

4

CLIPS> (integer -2)

-2

CLIPS>

12.5.2 Extended Math Functions

In addition to standard math functions, CLIPS also provides a large number of scien­tific and trigonometric math functions for more extensive computations. Although included in the generic version of CLIPS, if an expert system does not need these cap­a­bilities, these functions may be excluded from the executable element of CLIPS to pro­vide more memory (see the Advanced Programming Guide).


Portability Note

These mathematical functions use the C library math.h. If the user’s system does not sup­port this library, the user needs to make some adjustments to math.c. The system depen­dent math functions are called from CosFunction, SinFunction, etc. The user must change each of these to call the appropriate functions from his/her system. The user also must make sure that the func­tions CosFunction, SinFunction, etc., always return double precision floating point numbers. To link these func­tions, most compilers provide a separate math library that must be included during linking.

12.5.2.1 Trigonometric Functions

The following trigonometric functions take one numeric argument and return a floating point number. The argument is expected to be in radians.

  • FUNCTION RETURNS acos arccosine acosh hyperbolic arccosine acot arccotangent acoth hyperbolic arccotangent acsc arccosecant acsch hyperbolic arccosecant asec arcsecant asech hyperbolic arcsecant asin arcsine asinh hyperbolic arcsine atan arctangent atanh hyperbolic arctangent cos cosine cosh hyperbolic cosine cot cotangent coth hyperbolic tangent csc cosecant csch hyperbolic cosecant sec secant sech hyperbolic secant sin sine sinh hyperbolic sine tan tangent tanh hyperbolic tangent

Example

CLIPS> (cos 0)

1.0

CLIPS> (acos 1.0)

0.0

CLIPS>

12.5.2.2 Convert From Degrees to Grads

The deg grad function converts its only argument (which should be a numeric expression) from units of degrees to units of grads (360 degrees = 400 grads). The return value of this function is a float.

Syntax

(deg-grad <numeric-expression>)

Example

CLIPS> (deg-grad 90)

100.0

CLIPS>

12.5.2.3 Convert From Degrees to Radians

The deg rad function converts its only argument (which should be a numeric expression) from units of degrees to units of radians (360 degrees = 2π radians). The return value of this function is a float.

Syntax

(deg-rad <numeric-expression>)

Example

CLIPS> (deg-rad 180)

3.141592653589793

CLIPS>

12.5.2.4 Convert From Grads to Degrees

The grad deg function converts its only argument (which should be a numeric expression) from units of grads to units of degrees (360 degrees = 400 grads). The return value of this function is a float.

Syntax

(grad-deg <numeric-expression>)

Example

CLIPS> (grad-deg 100)

90.0

CLIPS>

12.5.2.5 Convert From Radians to Degrees

The rad deg function converts its only argument (which should be a numeric expression) from units of radians to units of degrees (360 degrees = 2π radians). The return value of this function is a float.

Syntax

(rad-deg <numeric-expression>)

Example

CLIPS> (rad-deg 3.141592653589793)

180.0

CLIPS>

12.5.2.6 Return the Value of π

The pi function returns the value of π (3.141592653589793…) as a float.

Syntax

(pi)

Example

CLIPS> (pi)

3.141592653589793

CLIPS>

12.5.2.7 Square Root

The sqrt function returns the square root of its only argument (which should be a numeric expression) as a float.

Syntax

(sqrt <numeric-expression>)

Example

CLIPS> (sqrt 9)

3.0

CLIPS>

12.5.2.8 Power

The ** function raises its first argument to the power of its second argument and returns this value as a float.

Syntax

(** <numeric-expression> <numeric-expression>)

Example

CLIPS> (** 3 2)

9.0

CLIPS>

12.5.2.9 Exponential

The exp function raises the value e (the base of the natural system of logarithms, having a value of approximately 2.718…) to the power specified by its only argument and returns this value as a float.

Syntax

(exp <numeric-expression>)

Example

CLIPS> (exp 1)

2.718281828459045

CLIPS>

12.5.2.10 Logarithm

Given n (the only argument) and the value e is the base of the natural system of logarithms, the log function returns the float value x such that the following equation is satisfied:


n = ex

Syntax

(log <numeric-expression>)

Example

CLIPS> (log 2.718281828459045)

0.9999999999999999

CLIPS>

12.5.2.11 Logarithm Base 10

Given n (the only argument), the log10 function returns the float value x such that the following equation is satisfied:


n = 10x

Syntax

(log10 <numeric-expression>)

Example

CLIPS> (log10 100)

2.0

CLIPS>

12.5.2.12 Round

The round function rounds its only argument (which should be a numeric expression) toward the closest integer. If the argument is exactly between two integers, it is rounded down. The return value of this function is an integer.

Syntax

(round <numeric-expression>)

Example

CLIPS> (round 3.6)

4

CLIPS>

12.5.2.13 Modulus

The mod function returns the remainder of the result of dividing its first argument by its second argument (assuming that the result of division must be an integer). It returns an integer if both arguments are integers, otherwise it returns a float.

Syntax

(mod <numeric-expression> <numeric-expression>)

Example

CLIPS> (mod 5 2)

1

CLIPS> (mod 3.7 1.2)

0.1

CLIPS>

12.6 Procedural Functions

The following are functions which provide procedural programming capabilities as found in languages such as Pascal, C and Ada.

12.6.1 Binding Variables

Occasionally, it is important to create new variables or to modify the value of previously bound variables on the RHS of a rule. The bind function provides this capability.

Syntax

(bind <variable> <expression>*)


where the first argument to bind, <variable>, is the local or global variable to be bound (it may have been bound previously). The bind function may also be used within a message handler's body to set a slot's value.


If no <expression> is specified, then local variables are unbound and global variables are reset to their original value. If one <expression> is specified, then the value of <variable> is set to the return value from evaluating <expression>. If more than one <expression> is specified, then all of the <expressions> are evaluated and grouped together as a multifield value and the resulting value is stored in <variable>.


The bind function returns the symbol FALSE when a local variable is unbound, otherwise, the return value is the value to which <variable> is set.

Example 1

CLIPS> (defglobal ?*x* = 3.4)

CLIPS> ?*x*

3.4

CLIPS> (bind ?*x* (+ 8 9))

17

CLIPS> ?*x*

17

CLIPS> (bind ?*x* (create$ a b c d))

(a b c d)

CLIPS> ?*x*

(a b c d)

CLIPS> (bind ?*x* d e f)

(d e f)

CLIPS> ?*x*

(d e f)

CLIPS> (bind ?*x*)

3.4

CLIPS> ?*x*

3.4

CLIPS>

Example 2

CLIPS>

(defclass A (is-a USER)

(role concrete)

(slot x) (slot y))

CLIPS>

(defmessage-handler A init after ()

(bind ?self:x 3)

(bind ?self:y 4))

CLIPS> (make-instance a of A)

[a]

CLIPS> (send [a] print)

[a] of A

(x 3)

(y 4)

CLIPS>

12.6.2 If...then...else Function

The if function provides an if…then…else structure to allow for conditional execution of a set of actions.

Syntax

(if <expression>
then
<action>*
[else
<action>*])


Any number of allowable actions may be used inside of the then or else portion, including another if…then…else structure. The else portion is optional. If <expression> evaluates to anything other than the symbol FALSE, then the actions associated with the then portion are executed. Otherwise, the actions associated with the else portion are executed. The return value of the if function is the value of the last <expression> or <action> evaluated.

Example

(defrule closed-valves
(temp high)
(valve ?v closed)

(if (= ?v 6)
then
(printout t “The special valve ” ?v ” is closed!” crlf)
(assert (perform special operation))
else
(printout t “Valve ” ?v ” is normally closed“ crlf)))


Note that this rule could have been accomplished just as easily with two rules, and that it is usually better to accomplish this with two rules.


(defrule closed-valves-number-6
(temp high)
(valve 6 closed)

(printout t “The special valve 6 is closed!” crlf)
(assert (perform special operation)))


(defrule closed-valves-other-than-6
(temp high)
(valve ?v&~6 closed)

(printout t “Valve ” ?v ” is normally closed“ crlf))

12.6.3 While

The while function is provided to allow simple looping. Its use is similar to that of the if function.

Syntax

(while <expression> [do]
<action>*)


Again, all predicate functions are available for use in while. Any number of allowable actions may be placed inside the while block, including if…then…else or ad­ditional while structures. The test is performed prior to the first execution of the loop. The actions within the while loop are executed until <expression> evaluates to the symbol FALSE. The while may optionally include the symbol do after the condition and before the first action. The break and return functions can be used to terminate the loop prematurely. The return value of this function is FALSE unless the return function is used to terminate the loop.

Example

(defrule open-valves
(valves-open-through ?v)

(while (> ?v 0)

(printout t “Valve ” ?v ” is open“ crlf)
(bind ?v (- ?v 1))))

12.6.4 Loop-for-count

The loop for count function is provided to allow simple iterative looping.

Syntax

(loop-for-count <range-spec> [do] <action>*)


<range-spec> ::= <end-index> |

(<loop-variable> <start-index> <end-index>) |

(<loop-variable> <end-index>)

<start-index> ::= <integer-expression>

<end-index> ::= <integer-expression>


Performs the given actions the number of times specified by <range spec>. If <start index> is not given, it is assumed to be one. If <start index> is greater than <end index>, then the body of the loop is never executed. The integer value of the current iteration can be examined with the loop variable, if specified.The break and return functions can be used to terminate the loop prematurely. The return value of this function is FALSE unless the return function is used to terminate the loop. Variables from an outer scope may be used within the loop, but the loop variable (if specified) masks any outer variables of the same name. Loops can be nested.

Example

CLIPS> (loop-for-count 2 (printout t “Hello world” crlf))

Hello world

Hello world

FALSE

CLIPS>

(loop-for-count (?cnt1 2 4) do

(loop-for-count (?cnt2 1 3) do

(printout t ?cnt1 ” “ ?cnt2 crlf)))

2 1

2 2

2 3

3 1

3 2

3 3

4 1

4 2

4 3

FALSE

CLIPS>

12.6.5 Progn

The progn function evaluates all of its arguments and returns the value of the last argument;.

Syntax

(progn <expression>*)

Example

CLIPS> (progn (setgen 5) (gensym))

gen5

CLIPS>

12.6.6 Progn$

The progn$ function performs a set of actions for each field of a multifield value. The field of the current iteration can be examined with <loop variable>, if specified. The index of the current iteration can be examined with <loop variable> index. The progn$ function can use variables from outer scopes, and the return and break functions can also be used within a progn$ as long as they are valid in the outer scope. The return value of this function is the return value of the last action performed for the last field in the multifield value.

Syntax

(progn$ <list-spec> <expression>*)


<list-spec> ::= <multifield-expression> |

(<list-variable> <multifield-expression>)

Example

CLIPS> (progn$ (?field (create$ abc def ghi))

(printout t ”–> “ ?field ” “ ?field-index ” ←-“ crlf))

–> abc 1 ←-

–> def 2 ←-

–> ghi 3 ←-

CLIPS>

12.6.7 Return

The return function immediately terminates the currently executing deffunction, generic function method, message handler, defrule RHS, or certain instance set query functions (do for instance, do for all instances and delayed do for all instances). Without any arguments, there is no return value. However, if an argument is included, its evaluation is given as the return value of the deffunction , method or message handler.


The return function can only be used within the actions of deffunctions, methods and message handlers, defrules, or the instance set query functions previously listed. If used on the RHS of a rule, the current focus is removed from the focus stack. In addition, return should not be used as an argument to another function call. If used within an instance set query function, the return function is only valid if it is applicable in the outer scope of the query.

Syntax

(return [<expression>])

Example

CLIPS>

(deffunction sign (?num)

(if (> ?num 0) then

(return 1))

(if (< ?num 0) then

(return -1))

0)

CLIPS> (sign 5)

1

CLIPS> (sign -10)

-1

CLIPS> (sign 0)

0

CLIPS>

12.6.8 Break

The break function immediately terminates the currently iterating while loop, loop-for-count execution, progn execution, progn$ execution, or certain instance set query functions (do for instance, do for all instances and delayed do for all instances).


The break function can only be used within the actions of a while loop, loop-for-count execution, progn execution, progn$ execution, or the specified instance set queries previously listed. Other uses will have no effect. The break cannot be used within a progn unless it is valid for the outer scope of the progn. In addition, break should not be used as an argument to another function call.

Syntax

(break)

Example

CLIPS>

(deffunction iterate (?num)

(bind ?i 0)

(while TRUE do

(if (>= ?i ?num) then

(break))

(printout t ?i ” “)

(bind ?i (+ ?i 1)))

(printout t crlf))

CLIPS> (iterate 1)

0

CLIPS> (iterate 10)

0 1 2 3 4 5 6 7 8 9

CLIPS>

12.6.9 Switch

The switch function allows a particular group of actions (among several groups of actions) to be performed based on a specified value.

Syntax

(switch <test-expression>

<case-statement>*

[<default-statement>])

<case-statement> ::=

(case <comparison-expression> then <action>*)

<default-statement> ::= (default <action>*)


As indicated by the BNF, the optional default statement must succeed all case statements. None of the case comparison expressions should be the same.


The switch function evaluates the <test expression> first and then evaluates each <comparison expression> in order of definition. Once the evaluation of the <comparison expression> is equivalent to the evaluation of the <test expression>, the actions of that case are evaluated (in order) and the switch function is terminated. If no cases are satisfied, the default actions (if any) are evaluated (in order).


The return value of the switch function is the last action evaluated in the switch function. If no actions are evaluated, the return value is the symbol FALSE.

Example


CLIPS> (defglobal ?*x* = 0)

CLIPS> (defglobal ?*y* = 1)

CLIPS>

(deffunction foo (?val)

(switch ?val

(case ?*x* then *x*)

(case ?*y* then *y*)

(default none)))

CLIPS> (foo 0)

*x*

CLIPS> (foo 1)

*y*

CLIPS> (foo 2)

none

CLIPS>

12.7 Miscellaneous Functions

The following are additional functions for use within CLIPS.

12.7.1 Gensym

The gensym function returns a special, sequenced symbol that can be stored as a sin­gle field. This is primarily for tagging patterns that need a unique identifier, but the user does not care what the identifier is. Multiple calls to gensym are guaranteed to return different identifiers of the form


genX


where X is a positive integer. The first call to gensym returns gen1; all subsequent calls increment the number. Note that gensym is not reset after a call to clear. If users plan to use the gensym feature, they should avoid creating facts which include a user defined field of this form.

Example

(assert (new-id (gensym) flag1 7))


which, on the first call, generates a fact of the form


(new-id gen1 flag1 7)

12.7.2 Gensym*

The gensym* function is similar to the gensym function, however, it will produce a unique symbol that does not currently exist within the CLIPS environment.

Example

CLIPS> (setgen 1)

1

CLIPS> (assert (gen1 gen2 gen3))

<Fact-0>

CLIPS> (gensym)

gen1

CLIPS> (gensym*)

gen4

CLIPS>

12.7.3 Setgen

The setgen function allows the user to set the starting number used by gensymand gensym* (see sections 12.7.1 and 12.7.2).

Syntax

(setgen <integer-expression>)


where <intger-expression> must be a positive integer value and is the value returned by this function. All subsequent calls to gensym will return a sequenced symbol with the numeric portion of the symbol starting at <integer-expression>.

Example

CLIPS> (setgen 32)

32

CLIPS>


After this, calls to gensym will return gen32, gen33, etc.

12.7.4 Random

The random function returns a “random” integer value. It is patterned after the ANSI standard rand library function and therefore may not be available on all platforms.

Syntax

(random [<start-integer-expression> <end-integer-expression>])


where <start-integer-expression> and <end-integer-expression> if specified indicate the range of values to which the randomly generated integer is limited.

Example

(defrule roll-the-dice
(roll-the-dice)

(bind ?roll1 (random 1 6))

(bind ?roll2 (random 1 6))

(printout t “Your roll is: ” ?roll1 ” “ ?roll2 crlf))



Portability Note

If the ANSI_COMPILER flag has not been set, this function compiles to a non functional stub that always returns zero.

12.7.5 Seed

The seed function seeds the random number generator. It is patterned after the ANSI standard seed library function and therefore may not be available on all platforms.

Syntax

(seed <integer-expression>)


where <integer-expression> is the integer seed value and the function has no return value.


Portability Note

If the ANSI_COMPILER flag has not been set, this function compiles to a non functional stub.

12.7.6 Time

The time function returns a floating point value representing the elapsed seconds since the system refer­ence time.

Syntax

(time)


Portability Note

Not all operating systems/compilers provide this function. The code is stored in the sysdep.c file, and the default coding for generic CLIPS is a non ­functional stub that returns zero for the time.

12.7.7 Number of Fields or Characters in a Data Object

The length function returns an integer for the number of fields bound to a multifield value or the length in characters of a string or symbol.

Syntax

(length <string-symbol-or-multifield-expression>)


If the argument given to length is not the appropriate type, a negative one ( 1) is returned. This function may also be called using the name length$.

Example

CLIPS> (length (create$ a b c d e f g))

7

CLIPS> (length “cat”)

3

CLIPS>

12.7.8 Determining the Restrictions for a Function

The get function restrictions function can be used to gain access to the restriction string associated with a CLIPS or user defined function. The restriction string contains information on the number and types of arguments that a function expects. See section 3.1 of the Advanced Programming Guide for the meaning of the characters which compose the restriction string.

Syntax

(get-function-restrictions <function-name>)

Example

CLIPS> (get-function-restrictions +)

“2*n”

CLIPS>

12.7.9 Sorting a List of Values

The function sort allows a list of values to be sorted based on a user specified comparison function.

Syntax

(sort <comparison-function-name> <expression>*)


This function returns a multifield value containing the sorted values specified as arguments. The comparison function used for sorting should accept exactly two arguments and can be a user-defined function, a generic function, or a deffunction. Given two adjacent arguments from the list to be sorted, the comparison function should return TRUE if its first argument should come after its second argument in the sorted list.

Example

CLIPS> (sort > 4 3 5 7 2 7)

(2 3 4 5 7 7)

CLIPS>

(deffunction string> (?a ?b)

(> (str-compare ?a ?b) 0))

CLIPS> (sort string> ax aa bk mn ft m)

(aa ax bk ft m mn)

CLIPS>

12.7.10 Calling a Function

The function funcall constructs a function call from its arguments and then evaluates the function call. The first argument should be the name of a user-defined function, deffunction, or generic function. The remaining arguments are evaluated and then passed to the specified function when it is evaluated.

Syntax

(funcall (function-name> <expression>*)

Example

CLIPS> (funcall + 1 (create$ 2 3) 4)

10

CLIPS>

12.7.11 Timing Functions and Commands

The function timer returns the number of seconds elapsed evaluating a series of expressions.

Syntax

(timer <expression>*)

Example

CLIPS> (timer (loop-for-count 10000 (+ 3 4)))

0.0416709999999512

CLIPS>

12.8 Deftemplate Functions

The following functions provide ancillary capabilities for the deftemplate construct.

12.8.1 Getting the List of Deftemplates

The function get deftemplate list returns a multifield value containing the names of all deftemplate constructs facts visible to the module specified by <module-name> or to the current module if none is specified. If * is specified as the module name, then all deftemplates are returned.

Syntax

(get deftemplate list [<module-name>])

Example

CLIPS> (clear)

CLIPS> (get-deftemplate-list)

()

CLIPS> (deftemplate foo)

CLIPS> (deftemplate bar)

CLIPS> (get-deftemplate-list)

(foo bar)

CLIPS>

12.8.2 Determining the Module in which a Deftemplate is Defined

This function returns the module in which the specified deftemplate name is defined.

Syntax

(deftemplate module <deftemplate-name>)

12.9 Fact Functions

The following actions are used for assert, retracting, and modifying facts.

12.9.1 Creating New Facts

Theassert action allows the user to add a fact to the fact list. Multiple facts may be asserted with each call. If the facts item is being watched (see section 13.2), then an informational message will be printed each time a fact is asserted.

Syntax

(assert <RHS-pattern>+)


Missing slots in a tem­plate fact being asserted are assigned their default value (see section 3). If an identical copy of the fact already exists in the fact list, the fact will not be added (however, this behavior can be changed, see sections 13.4.4 and 13.4.5). Note that in addition to constants, expressions can be placed within a fact to be asserted. The first field of a fact must be a symbol. The value returned of the assert function is the fact address of the last fact asserted. If the assertion of the last fact causes an error, or if an identical copy of the fact already exists in the fact list, then the symbol FALSE is returned.

Example

CLIPS> (clear)

CLIPS> (assert (color red))

<Fact-0>

CLIPS> (assert (color blue) (value (+ 3 4)))

<Fact-2>

CLIPS> (assert (color red))

FALSE

CLIPS> (deftemplate status (slot temp) (slot pressure))

CLIPS> (assert (status (temp high)

(pressure low)))

<Fact-3>

CLIPS> (facts)

f-0 (color red)

f-1 (color blue)

f-2 (value 7)

f-3 (status (temp high) (pressure low))

For a total of 4 facts.

CLIPS>

12.9.2 Removing Facts from the Fact list

The retract action allows the user to remove facts from the fact list. Multiple facts may be retracted with a single retract statement. The retraction of a fact also removes all rules that depended upon that fact for activation from the agenda. Retraction of a fact may also cause the retraction of other facts which receive logical support from the retracted fact. If the facts item is being watched (see section 13.2), then an informational message will be printed each time a fact is retracted.

Syntax

(retract <retract-specifier>+ | *)


<retract-specifier> ::= <fact-specifier> | <integer-expression>


The term <retract specifier> includes variables bound on the LHS to fact addresses as described in section 5.4.1.8, or the fact index of the desired fact (e.g. 3 for the fact labeled f 3), or an expression which evaluates to a retract specifier. If the symbol * is used as an argument, all facts will be retracted. Note that the number generally is not known during the execution of a program, so facts usually are retracted by binding them on the LHS of a rule. Only variable;s, fact indices, or the symbol * may be used in a re­tract. External functions may not be called. This function has no return value.

Example

(defrule change-valve-status
?f1 ← (valve ?v open)
?f2 ← (set ?v close)

(retract ?f1 ?f2)
(assert (valve ?v close)))

12.9.3 Modifying Template Facts

The modify action allows the user to modify template facts on the fact list. Only one fact may be modified with a single modify statement. The modification of a fact is equivalent to retracting the present fact and asserting the modified fact. Therefore, any facts receiving logical support from a template fact are retracted (assuming no other support) when the template fact is modified and the new template fact loses any logical support that it previously had.

Syntax

(modify <fact-specifier> <RHS-slot>*)


The term <fact specifier> includes variables bound on the LHS to fact addresses as described in section 5.4.1.8 or the fact index of the desired fact (e.g. 3 for the fact labeled f 3). Note that the fact index generally is not known during the execution of a program, so facts usually are modified by binding them on the LHS of a rule. Static deftemplate checking is not performed when a fact index is used as the <fact specifier> since the deftemplate being referenced is usually ambiguous. Only variables or fact indices may be used in a modify. External functions may not be called. The value returned by this function is the fact address of the newly modified fact. If the assertion of the newly modified fact causes an error, or if an identical copy of the newly modified fact already exists in the fact list, then the symbol FALSE is returned.

Example

(defrule change-valve-status
?f1←(status (valve open))
?f2←(close-valve)

(retract ?f2)
(modify ?f1 (valve closed)))

12.9.4 Duplicating Template Facts

The duplicate action allows the user to duplicate deftemplate facts on the fact list changing a group of specified fields. This command allows a new fact to be created by copying most of the fields of a source fact and then specifying the fields to be changed. Only one fact may be duplicated with a single duplicate statement. The duplicate command is similar to the modify command except the fact being duplicated is not retracted.

Syntax

(duplicate <fact-specifier> <RHS-slot>*)


The term <fact specifier> includes variables bound on the LHS to fact addresses as described in section 5.4.1.8 or the fact index of the desired fact (e.g. 3 for the fact labeled f 3). Note that the fact index generally is not known during the execution of a program, so facts usually are duplicated by binding them on the LHS of a rule. Static deftemplate checking is not performed when a fact index is used as the <fact specifier> since the deftemplate being referenced is usually ambiguous. Only variables or fact indices may be used in a duplicate. External functions may not be called. The value returned by this function is the fact address of the newly duplicated fact. If the assertion of the newly duplicated fact causes an error, or if an identical copy of the newly duplicated fact already exists in the fact list, then the symbol FALSE is returned.

Example

(defrule duplicate-part
?f1 ← (duplicate-part ?name)
?f2 ← (part (name ?name))

(retract ?f1)
(duplicate ?f2 (id (gensym*))))

12.9.5 Asserting a String

Theassert string function is similar to assert in that it will add a fact to the fact list. How­ever, assert string takes a single string representing a fact (expressed in either ordered or deftemplate format ) and asserts it. Only one fact may be asserted with each assert string statement.

Syntax

(assert-string <string-expression>)


If an identical copy of the fact already exists in the fact list, the fact will not be added (however, this behavior can be changed, see sections 13.4.4 and 13.4.5). Fields within the fact may contain a string by escaping the quote character with a backslash. Note that this function takes a string and turns it into fields. If the fields within that string are going to contain special characters (such as a backslash), they need to be escaped twice (because you are literally embedding a string within a string and the backslash mechanism ends up being applied twice). Global variables and expressions can be contained within the string. The value returned by this function is the fact address of the newly created fact. If the assertion of the newly created fact causes an error, or if an identical copy of the newly created fact already exists in the fact list, then the symbol FALSE is returned.

Example

CLIPS> (clear)

CLIPS> (deftemplate foo (slot x) (slot y))

CLIPS> (assert-string ”(status valve open)“)

CLIPS> (assert-string ”(light \“red\”)“)

CLIPS> (assert-string ”(a\\b \“c\\\\d\”)“)

CLIPS> (assert-string ”(foo (x 3))“)

CLIPS> (assert-string ”(foo (y 7))“)

CLIPS> (facts)

f-0 (status valve open)

f-1 (light “red”)

f-2 (a\b “c\d”)

f-3 (foo (x 3) (y nil))

f-4 (foo (x nil) (y 7))

For a total of 5 facts.

CLIPS>

12.9.6 Getting the Fact Index of a Fact address

The fact index function returns the fact index (an integer) of a fact address.

Syntax

(fact-index <fact-address>)

Example

(defrule print-fact-indices
?f ← (some-fact $?)

(printout t (fact-index ?f) crlf))

12.9.7 Determining If a Fact Exists

The fact existp returns TRUE if the fact specified by its fact-index or fact-address arguments exists, otherwise FALSE is returned.

Syntax

(fact-existp <fact-address-or-index>)

Example

CLIPS> (clear)

CLIPS> (defglobal ?*x* = (assert (example fact)))

CLIPS> (facts)

f-0 (example fact)

For a total of 1 fact.

CLIPS> (fact-existp 0)

TRUE

CLIPS> (retract 0)

CLIPS> (fact-existp ?*x*)

FALSE

CLIPS>

12.9.8 Determining the Deftemplate (Relation) Name Associated with a Fact

The fact relation function returns the deftemplate (relation) name associated with the fact. FALSE is returned if the specified fact does not exist.

Syntax

(fact-relation <fact-address-or-index>)

Example

CLIPS> (clear)

CLIPS> (assert (example fact))

<Fact-0>

CLIPS> (fact-relation 0)

example

CLIPS>

12.9.9 Determining the Slot Names Associated with a Fact

The fact slot-names function returns the slot names associated with the fact in a multifield value. The symbol implied is returned for an ordered fact (which has a single implied multifield slot). FALSE is returned if the specified fact does not exist.

Syntax

(fact-slot-names <fact-address-or-index>)

Example

CLIPS> (clear)

CLIPS> (deftemplate foo (slot bar) (multislot yak))

CLIPS> (assert (foo (bar 1) (yak 2 3)))

<Fact-0>

CLIPS> (fact-slot-names 0)

(bar yak)

CLIPS> (assert (another a b c))

<Fact-1>

CLIPS> (fact-slot-names 1)

(implied)

CLIPS>

12.9.10 Retrieving the Slot Value of a Fact

The fact slot-value function returns the value of the specified slot from the specified fact. The symbol implied should be used as the slot name for the implied multifield slot of an ordered fact. FALSE is returned if the slot name argument is invalid or the specified fact does not exist.

Syntax

(fact-slot-value <fact-address-or-index> <slot-name>)

Example

CLIPS> (clear)

CLIPS> (deftemplate foo (slot bar) (multislot yak))

CLIPS> (assert (foo (bar 1) (yak 2 3)))

<Fact-0>

CLIPS> (fact-slot-value 0 bar)

1

CLIPS> (fact-slot-value 0 yak)

(2 3)

CLIPS> (assert (another a b c))

<Fact-1>

CLIPS> (fact-slot-value 1 implied)

(a b c)

CLIPS>

12.9.11 Retrieving the Fact-List

The get-fact-list function returns a multifield containing the list of facts visible to the module specified by <module-name> or to the current module if none is specified. If * is specified as the module name, then all facts are returned.

Syntax

(get-fact-list [<module-name>])

Example

CLIPS> (clear)

CLIPS> (assert (a))

<Fact-0>

CLIPS> (get-fact-list)

(<Fact-0>)

CLIPS> (defmodule B)

CLIPS> (assert (b))

<Fact-1>

CLIPS> (get-fact-list)

(<Fact-1>)

CLIPS> (get-fact-list MAIN)

(<Fact-0>)

CLIPS> (get-fact-list *)

(<Fact-0> <Fact-1>)

CLIPS>

12.10 Deffacts Functions

The following functions provide ancillary capabilities for the deffacts construct.

12.10.1 Getting the List of Deffacts

The function get deffacts list returns a multifield value containing the names of all deffacts constructs visible to the module specified by <module-name> or to the current module if none is specified. If * is specified as the module name, then all deffacts are returned.

Syntax

(get deffacts list [<module-name>])

Example

CLIPS> (clear)

CLIPS> (get-deffacts-list)

(initial-fact)

CLIPS> (deffacts foo)

CLIPS> (get-deffacts-list)

(initial-fact foo)

CLIPS>

12.10.2 Determining the Module in which a Deffacts is Defined

This function returns the module in which the specified deffacts name is defined.

Syntax

(deffacts module <deffacts-name>)

12.11 Defrule Functions

The following functions provide ancillary capabilities for the defrule construct.

12.11.1 Getting the List of Defrules

The function get defrule list returns a multifield value containing the names of all defrule constructs visible to the module specified by <module-name> or to the current module if none is specified. If * is specified as the module name, then all defrules are returned.

Syntax

(get defrule list)

Example

CLIPS> (clear)

CLIPS> (get-defrule-list)

()

CLIPS> (defrule foo ⇒)

CLIPS> (defrule bar ⇒)

CLIPS> (get-defrule-list)

(foo bar)

CLIPS>

12.11.2 Determining the Module in which a Defrule is Defined

This function returns the module in which the specified defrule name is defined.

Syntax

(defrule module <defrule-name>)

12.12 Agenda Functions

The following functions provide ancillary capabilities manipulating the agenda.

12.12.1 Getting the Current Focus

The function get focus returns the module name of the current focus. If the focus stack is empty, then the symbol FALSE is returned.

Syntax

(get focus)

Example

CLIPS> (clear)

CLIPS> (get-focus)

MAIN

CLIPS> (defmodule A)

CLIPS> (defmodule B)

CLIPS> (focus A B)

TRUE

CLIPS> (get-focus)

A

CLIPS>

12.12.2 Getting the Focus Stack

The function get focus stack returns all of the module names in the focus stack as a multifield value. A multifield value of length zero is returned if the focus stack is empty.

Syntax

(get focus stack)

Example

CLIPS> (clear)

CLIPS> (get-focus-stack)

(MAIN)

CLIPS> (clear-focus-stack)

CLIPS> (get-focus-stack)

()

CLIPS> (defmodule A)

CLIPS> (defmodule B)

CLIPS> (focus A B)

TRUE

CLIPS> (get-focus-stack)

(A B)

CLIPS>

12.12.3 Removing the Current Focus from the Focus Stack

The function pop focus removes the current focus from the focus stack and returns the module name of the current focus. If the focus stack is empty, then the symbol FALSE is returned.

Syntax

(pop focus)

Example

CLIPS> (clear)

CLIPS> (list-focus-stack)

MAIN

CLIPS> (pop-focus)

MAIN

CLIPS> (defmodule A)

CLIPS> (defmodule B)

CLIPS> (focus A B)

TRUE

CLIPS> (list-focus-stack)

A

B

MAIN

CLIPS> (pop-focus)

A

CLIPS> (list-focus-stack)

B

CLIPS>

12.13 Defglobal Functions

The following functions provide ancillary capabilities for the defglobal construct.

12.13.1 Getting the List of Defglobals

The function get defglobal list returns a multifield value containing the names of all global variables visible to the module specified by <module-name> or to the current module if none is specified. If * is specified as the module name, then all globals are returned.

Syntax

(get defglobal list [<module-name>])

Example

CLIPS> (clear)

CLIPS> (get-defglobal-list)

()

CLIPS> (defglobal ?*x* = 3 ?*y* = 5)

CLIPS> (get-defglobal-list)

(x y)

CLIPS>

12.13.2 Determining the Module in which a Defglobal is Defined

This function returns the module in which the specified defglobal name is defined.

Syntax

(defglobal module <defglobal-name>)

12.14 Deffunction Functions

The following functions provide ancillary capabilities for the deffunction construct.

12.14.1 Getting the List of Deffunctions

The function get deffunction list returns a multifield value containing the names of all deffunction constructs visible to the module specified by <module-name> or to the current module if none is specified. If * is specified as the module name, then all deffunctions are returned.

Syntax

(get deffunction list [<module-name>])

Example

CLIPS> (clear)

CLIPS> (get-deffunction-list)

()

CLIPS> (deffunction foo ())

CLIPS> (deffunction bar ())

CLIPS> (get-deffunction-list)

(foo bar)

CLIPS>

12.14.2 Determining the Module in which a Deffunction is Defined

This function returns the module in which the specified deffunction name is defined.

Syntax

(deffunction module <deffunction-name>)

12.15 Generic Function Functions

The following functions provide ancillary capabilities for generic function methods.

12.15.1 Getting the List of Defgenerics

The function get defgeneric list returns a multifield value containing the names of all defgeneric constructs that are currently defined.

Syntax

(get defgeneric list)

Example

CLIPS> (clear)

CLIPS> (get-defgeneric-list)

()

CLIPS> (defgeneric foo)

CLIPS> (defgeneric bar)

CLIPS> (get-defgeneric-list)

(foo bar)

CLIPS>

12.15.2 Determining the Module in which a Generic Function is Defined

This function returns the module in which the specified defgeneric name is defined.

Syntax

(defgeneric module <defgeneric-name>)

12.15.3 Getting the List of Defmethods

The function get defmethod list returns a multifield value containing method name/indices pairs for all defmethod constructs that are currently defined. The optional generic function name parameter restricts the methods return to only those of the specified generic function.

Syntax

(get defmethod list [<generic-function-name>])

Example

CLIPS> (clear)

CLIPS> (get-defmethod-list)

()

CLIPS> (defmethod foo ((?x STRING)))

CLIPS> (defmethod foo ((?x INTEGER)))

CLIPS> (defmethod bar ((?x STRING)))

CLIPS> (defmethod bar ((?x INTEGER)))

CLIPS> (get-defmethod-list)

(foo 1 foo 2 bar 1 bar 2)

CLIPS> (get-defmethod-list foo)

(foo 1 foo 2)

CLIPS>

12.15.4 Type Determination

The function type returns a symbol which is the name of the type (or class) of its of argument. This function is equivalent to the class function (see section 12.16.4.4), but, unlike the class function, it is available even when COOL is not installed.

Syntax

(type <expression>)

Example

CLIPS> (type (+ 2 2))

INTEGER

CLIPS> (defclass CAR (is-a USER) (role concrete))

CLIPS> (make-instance Rolls-Royce of CAR)

[Rolls-Royce]

CLIPS> (type Rolls-Royce)

SYMBOL

CLIPS> (type [Rolls-Royce])

CAR

CLIPS>

12.15.5 Existence of Shadowed Methods

If called from a method for a generic function, the function next methodp will return the symbol TRUE if there is another method shadowed (see section 8.5.3) by the current one. Otherwise, the function will return the symbol FALSE.

Syntax

(next methodp)

12.15.6 Calling Shadowed Methods

If the conditions are such that the function next methodpwould return the symbol TRUE (see section 12.15.5), then calling the function call next method will execute the shadowed (see section 8.5.3) method. Otherwise, a method execution error will occur (see section 8.5.4). In the event of an error, the return value of this function is the symbol FALSE, otherwise it is the return value of the shadowed method. The shadowed method is passed the same arguments as the calling method.


A method may continue execution after calling call next method. In addition, a method may make multiple calls to call next method, and the same shadowed method will be executed each time.

Syntax

(call next method)

Example

CLIPS>

(defmethod describe ((?a INTEGER))

(if (next-methodp) then

(bind ?extension (str-cat ” “ (call-next-method)))

else

(bind ?extension ”“))

(str-cat “INTEGER” ?extension))

CLIPS> (describe 3)

“INTEGER”

CLIPS>

(defmethod describe ((?a NUMBER))

“NUMBER”)

CLIPS> (describe 3)

“INTEGER NUMBER”

CLIPS> (describe 3.0)

“NUMBER”

CLIPS>

12.15.7 Calling Shadowed Methods with Overrides

The function override next method is similar to call next method, except that new arguments can be provided. This allows one method to act as a wrapper for another and set up a special environment for the shadowed method. From the set of methods which are more general than the currently executing one, the most specific method which is applicable to the new arguments is executed. (In contrast, call next method calls the next most specific method which is applicable to the same arguments as the currently executing one received.) A recursive call to the generic function itself should be used in lieu of override next method if the most specific of all methods for the generic function which is applicable to the new arguments should be executed.

Syntax

(override next method <expression>*)

Example

CLIPS> (clear)

CLIPS>

(defmethod + ((?a INTEGER) (?b INTEGER))

(override-next-method (* ?a 2) (* ?b 3)))

CLIPS> (list-defmethods +)

+ #2 (INTEGER) (INTEGER)

+ #SYS1 (NUMBER) (NUMBER) ($? NUMBER)

For a total of 2 methods.

CLIPS> (preview-generic + 1 2)

+ #2 (INTEGER) (INTEGER)

+ #SYS1 (NUMBER) (NUMBER) ($? NUMBER)

CLIPS> (watch methods)

CLIPS> (+ 1 2)

MTH » +:#2 ED:1 (1 2)

MTH » +:#SYS1 ED:2 (2 6)

MTH « +:#SYS1 ED:2 (2 6)

MTH « +:#2 ED:1 (1 2)

8

CLIPS> (unwatch methods)

CLIPS>

12.15.8 Calling a Specific Method

The function call specific method allows the user to call a particular method of a generic function without regards to method precedence. This allows the user to bypass method precedence when absolutely necessary. The method must be applicable to the arguments passed. Shadowed methods can still be called via call next method and override next method.

Syntax

(call specific method <generic-function> <method-index>

<expression>*)

Example

CLIPS> (clear)

CLIPS>

(defmethod + ((?a INTEGER) (?b INTEGER))

(* (- ?a ?b) (- ?b ?a)))

CLIPS> (list-defmethods +)

+ #2 (INTEGER) (INTEGER)

+ #SYS1 (NUMBER) (NUMBER) ($? NUMBER)

For a total of 2 methods.

CLIPS> (preview-generic + 1 2)

+ #2 (INTEGER) (INTEGER)

+ #SYS1 (NUMBER) (NUMBER) ($? NUMBER)

CLIPS> (watch methods)

CLIPS> (+ 1 2)

MTH » +:#2 ED:1 (1 2)

MTH « +:#2 ED:1 (1 2)

-1

CLIPS> (call-specific-method + 1 1 2)

MTH » +:#SYS1 ED:1 (1 2)

MTH « +:#SYS1 ED:1 (1 2)

3

CLIPS> (unwatch methods)

CLIPS>

12.15.9 Getting the Restrictions of Defmethods

The function get method restrictions returns a multifield value containing information about the restrictions for the specified method using the following format:


<minimum-number-of-arguments>

<maximum-number-of-arguments> (can be -1 for wildcards)

<number-of-restrictions>

<multifield-index-of-first-restriction-info>

.

.

.

<multifield-index-of-nth-restriction-info>

<first-restriction-query> (TRUE or FALSE)

<first-restriction-class-count>

<first-restriction-first-class>

.

.

.

<first-restriction-nth-class>

.

.

.

<mth-restriction-class-count>

<mth-restriction-first-class>

.

.

.

<mth-restriction-nth-class>


Syntax

(get method restrictions <generic-function-name>

<method-index>)

Example

CLIPS> (clear)

CLIPS>

(defmethod foo 50 ((?a INTEGER SYMBOL) (?b (= 1 1)) $?c))

CLIPS> (get-method-restrictions foo 50)

(2 -1 3 7 11 13 FALSE 2 INTEGER SYMBOL TRUE 0 FALSE 0)

CLIPS>

12.16 CLIPS Object-Oriented Language (COOL) Functions

The following functions provide ancillary capabilities for COOL.

12.16.1 Class Functions

12.16.1.1 Getting the List of Defclasses

The function get defclass list returns a multifield value containing the names of all defclass constructs visible to the module specified by <module-name> or to the current module if none is specified. If * is specified as the module name, then all defclasses are returned.

Syntax

(get defclass list [<module-name>])

Example

CLIPS> (clear)

CLIPS> (get-defclass-list)

(FLOAT INTEGER SYMBOL STRING MULTIFIELD EXTERNAL-ADDRESS FACT-ADDRESS INSTANCE-ADDRESS INSTANCE-NAME OBJECT PRIMITIVE NUMBER LEXEME ADDRESS INSTANCE USER INITIAL-OBJECT)

CLIPS> (defclass FOO (is-a USER))

CLIPS> (defclass BAR (is-a USER))

CLIPS> (get-defclass-list)

(FLOAT INTEGER SYMBOL STRING MULTIFIELD EXTERNAL-ADDRESS FACT-ADDRESS INSTANCE-ADDRESS INSTANCE-NAME OBJECT PRIMITIVE NUMBER LEXEME ADDRESS INSTANCE USER INITIAL-OBJECT FOO BAR)

CLIPS>

12.16.1.2 Determining the Module in which a Defclass is Defined

This function returns the module in which the specified defclass name is defined.

Syntax

(defclass module <defclass-name>)

12.16.1.3 Determining if a Class Exists

This function returns the symbol TRUE if the specified class is defined, FALSE otherwise.

Syntax

(class existp <class-name>)

12.16.1.4 Superclass Determination

This function returns the symbol TRUE if the first class is a superclass of the second class, FALSE otherwise.

Syntax

(superclassp <class1-name> <class2-name>)

12.16.1.5 Subclass Determination

This function returns the symbol TRUE if the first class is a subclass of the second class, FALSE otherwise.

Syntax

(subclassp <class1-name> <class2-name>)

12.16.1.6 Slot Existence

This function returns the symbol TRUE if the specified slot is present class, FALSE otherwise. If the inherit keyword is specified then the slot may be inherited, otherwise it must be directly defined in the specified class.

Syntax

(slot-existp <class> <slot> [inherit])

12.16.1.7 Testing whether a Slot is Writable

This function returns the symbol TRUE if the specified slot in the specified class is writable (see section 9.3.3.4). Otherwise, it returns the symbol FALSE. An error is generated if the specified class or slot does not exist.

Syntax

(slot writablep <class-expression> <slot-name-expression>)

12.16.1.8 Testing whether a Slot is Initializable

This function returns the symbol TRUE if the specified slot in the specified class is initializable (see section 9.3.3.4). Otherwise, it returns the symbol FALSE. An error is generated if the specified class or slot does not exist.

Syntax

(slot initablep <class-expression> <slot-name-expression>)

12.16.1.9 Testing whether a Slot is Public

This function returns the symbol TRUE if the specified slot in the specified class is public (see section 9.3.3.8). Otherwise, it returns the symbol FALSE. An error is generated if the specified class or slot does not exist.

Syntax

(slot publicp <class-expression> <slot-name-expression>)

12.16.1.10 Testing whether a Slot can be Accessed Directly

This function returns the symbol TRUE if the specified slot in the specified class can be accessed directly (see section 9.3.3.4). Otherwise, it returns the symbol FALSE. An error is generated if the specified class or slot does not exist.

Syntax

(slot direct accessp <class-expression> <slot-name-expression>)

12.16.1.11 Message handler Existence

This function returns the symbol TRUE if the specified message handler is defined (directly only, not by inheritance) for the class, FALSE otherwise.

Syntax

Defaults are outlined.


(message handler existp <class-name> <handler-name> [<handler-type>])

<handler-type> ::= around | before | primary | after

12.16.1.12 Determining if a Class can have Direct Instances

This function returns the symbol TRUE if the specified class is abstract, i.e. the class cannot have direct instances, FALSE otherwise.

Syntax

(class abstractp <class-name>)

12.16.1.13 Determining if a Class can Satisfy Object Patterns

This function returns the symbol TRUE if the specified class is reactive, i.e. objects of the class can match object patterns, FALSE otherwise.

Syntax

(class reactivep <class-name>)

12.16.1.14 Getting the List of Superclasses for a Class

This function groups the names of the direct superclasses of a class into a multifield variable. If the optional argument “inherit” is given, indirect superclasses are also included. A multifield of length zero is returned if an error occurs.

Syntax

(class superclasses <class-name> [inherit])

Example

CLIPS> (class-superclasses INTEGER)

(NUMBER)

CLIPS> (class-superclasses INTEGER inherit)

(NUMBER PRIMITIVE OBJECT)

CLIPS>

12.16.1.15 Getting the List of Subclasses for a Class

This function groups the names of the direct subclasses of a class into a multifield variable. If the optional argument “inherit” is given, indirect subclasses are also included. A multifield of length zero is returned if an error occurs.

Syntax

(class subclasses <class-name> [inherit])

Example

CLIPS> (class-subclasses PRIMITIVE)

(NUMBER LEXEME MULTIFIELD EXTERNAL-ADDRESS)

CLIPS> (class-subclasses PRIMITIVE inherit)

(NUMBER INTEGER FLOAT LEXEME SYMBOL STRING MULTIFIELD ADDRESS EXTERNAL-ADDRESS FACT-ADDRESS INSTANCE-ADDRESS INSTANCE INSTANCE-NAME)

CLIPS>

12.16.1.16 Getting the List of Slots for a Class

This function groups the names of the explicitly defined slots of a class into a multifield variable. If the optional argument “inherit” is given, inherited slots are also included. A multifield of length zero is returned if an error occurs.

Syntax

(class slots <class-name> [inherit])

Example

CLIPS> (defclass A (is-a USER) (slot x))

CLIPS> (defclass B (is-a A) (slot y))

CLIPS> (class-slots B)

(y)

CLIPS> (class-slots B inherit)

(x y)

CLIPS>

12.16.1.17 Getting the List of Message Handlers for a Class

This function groups the class names, message names and message types of the message handlers attached direct to class into a multifield variable (implicit slot accessors are not included). If the optional argument “inherit” is given, inherited message handlers are also included. A multifield of length zero is returned if an error occurs.

Syntax

(get defmessage handler list <class-name> [inherit])

Example

CLIPS> (clear)

CLIPS> (defclass A (is-a USER))

CLIPS> (defmessage-handler A foo ())

CLIPS> (get-defmessage-handler-list A)

(A foo primary)

CLIPS> (get-defmessage-handler-list A inherit)

(USER init primary USER delete primary USER create primary USER print primary USER direct-modify primary USER message-modify primary USER direct-duplicate primary USER message-duplicate primary A foo primary)

CLIPS>

12.16.1.18 Getting the List of Facets for a Slot

This function returns a multifield listing the facet values for the specified slot (the slot can be inherited or explicitly defined for the class). A multifield of length zero is returned if an error occurs. Following is a table indicating what each field represents and its possible values:


| Field | Meaning | Values | Explanation |

1 Field Type SGL/MLT Single field or multifield
2 Default Value STC/DYN/NIL Static, dynamic or none
3 Inheritance INH/NIL Inheritable by other classes or not
4 Access RW/R/INT Read write, read only or initialize only
5 Storage LCL/SHR Local or shared
6 Pattern Match RCT/NIL Reactive or non reactive
7 Source EXC/CMP Exclusive or composite
8 Visibility PUB/PRV Public or private
9 Automatic Accessors R/W/RW/NIL Read, write, read-write or none
10 Override-Message <message-name> Name of message sent for slot overrides


See section 9.3.3 for more details on slot facets.

Syntax

(slot facets <class-name> <slot-name>)

Example

CLIPS> (clear)

CLIPS> (defclass A (is-a USER) (slot x (access read-only)))

CLIPS> (defclass B (is-a A) (multislot y))

CLIPS> (slot-facets B x)

(SGL STC INH R LCL RCT EXC PRV NIL NIL)

CLIPS> (slot-facets B y)

(MLT STC INH RW LCL RCT EXC PRV NIL put-y)

CLIPS>

12.16.1.19 Getting the List of Source Classes for a Slot

This function groups the names of the classes which provide facets for a slot of a class into a multifield variable. In the case of an exclusive slot, this multifield will be of length one and contain the name of the contributing class. However, composite slots may have facets from many different classes (see section 9.3.3.6). A multifield of length zero is returned if an error occurs.

Syntax

(slot sources <class-name> <slot-name>)

Example

CLIPS> (clear)

CLIPS>

(defclass A (is-a USER)

(slot x (access read-only)))

CLIPS>

(defclass B (is-a A)

(slot x (source composite)

(default 100)))

CLIPS> (defclass C (is-a B))

CLIPS> (slot-sources A x)

(A)

CLIPS> (slot-sources B x)

(A B)

CLIPS> (slot-sources C x)

(A B)

CLIPS>

12.16.1.20 Getting the Primitive Types for a Slot

This function groups the names of the primitive types allowed for a slot into a multifield variable. A multifield of length zero is returned if an error occurs.

Syntax

(slot types <class-name> <slot-name>)

Example

CLIPS> (clear)

CLIPS> (defclass A (is-a USER) (slot y (type INTEGER LEXEME)))

CLIPS> (slot-types A y)

(INTEGER SYMBOL STRING)

CLIPS>

12.16.1.21 Getting the Cardinality for a Slot

This function groups the minimum and maximum cardinality allowed for a multifield slot into a multifield variable. A maximum cardinality of infinity is indicated by the symbol +oo (the plus character followed by two lowercase o’s—not zeroes). A multifield of length zero is returned for single field slots or if an error occurs.

Syntax

(slot cardinality <class-name> <slot-name>)

Example

CLIPS> (clear)

CLIPS>

(defclass A (is-a USER)

(slot x)

(multislot y (cardinality ?VARIABLE 5))

(multislot z (cardinality 3 ?VARIABLE)))

CLIPS> (slot-cardinality A x)

()

CLIPS> (slot-cardinality A y)

(0 5)

CLIPS> (slot-cardinality A z)

(3 +oo)

CLIPS>

12.16.1.22 Getting the Allowed Values for a Slot

This function groups the allowed values for a slot (specified in any of allowed … facets for the slots) into a multifield variable. If no allowed … facets were specified for the slot, then the symbol FALSE is returned. A multifield of length zero is returned if an error occurs.

Syntax

(slot allowed values <class-name> <slot-name>)

Example

CLIPS> (clear)

CLIPS>

(defclass A (is-a USER)

(slot x)

(slot y (allowed-integers 2 3) (allowed-symbols foo)))

CLIPS> (slot-allowed-values A x)

FALSE

CLIPS> (slot-allowed-values A y)

(2 3 foo)

CLIPS>

12.16.1.23 Getting the Numeric Range for a Slot

This function groups the minimum and maximum numeric ranges allowed a slot into a multifield variable. A minimum value of infinity is indicated by the symbol  oo (the minus character followed by two lowercase o’s—not zeroes). A maximum value of infinity is indicated by the symbol +oo (the plus character followed by two lowercase o’s—not zeroes). The symbol FALSE is returned for slots in which numeric values are not allowed. A multifield of length zero is returned if an error occurs.

Syntax

(slot range <class-name> <slot-name>)

Example

CLIPS> (clear)

CLIPS>

(defclass A (is-a USER)

(slot x)

(slot y (type SYMBOL))

(slot z (range 3 10)))

CLIPS> (slot-range A x)

(-oo +oo)

CLIPS> (slot-range A y)

FALSE

CLIPS> (slot-range A z)

(3 10)

CLIPS>

12.16.1.24 Getting the Default Value for a Slot

This function returns the default value associated with a slot. If a slot has a dynamic default, the expression will be evaluated when this function is called. The symbol FALSE is returned if an error occurs.

Syntax

(slot default-value <class-name> <slot-name>)

Example

CLIPS> (clear)

CLIPS>

(defclass A (is-a USER)

(slot x (default 3))

(multislot y (default a b c))

(slot z (default-dynamic (gensym))))

CLIPS> (slot-default-value A x)

3

CLIPS> (slot-default-value A y)

(a b c)

CLIPS> (slot-default-value A z)

gen1

CLIPS> (slot-default-value A z)

gen2

CLIPS>

12.16.1.25 Setting the Defaults Mode for Classes

This function sets the defaults mode used when classes are defined. The old mode is the return value of this function.

Syntax

(set class-defaults-mode <mode>)


where <mode> is either convenience or conservation. By default, the class defaults mode is convenience. If the mode is convenience, then for the purposes of role inheritance, system defined class behave as concrete classes; for the purpose of pattern-match inheritance, system defined classes behave as reactive classes unless the inheriting class is abstract; and the default setting for the create-accessor facet of the class’ slots is read write. If the class defaults mode is conservation, then the role and reactivity of system-defined classes is unchanged for the purposes of role and pattern-match inheritance and the default setting for the create-accessor facet of the class’ slots is ?NONE.

12.16.1.26 Getting the Defaults Mode for Classes

This function returns the current defaults mode used when classes are defined (convenience or conservation).

Syntax

(get class-defaults-mode)

12.16.2 Message handler Functions

12.16.2.1 Existence of Shadowed Handlers

This function returns the symbol TRUE if there is another message handler available for execution, FALSE otherwise. If this function is called from an around handler and there are any shadowed handlers (see section 9.5.3), the return value is the symbol TRUE. If this function is called from a primary handler and there are any shadowed primary handlers, the return value is the symbol TRUE. In any other circumstance, the return value is the symbol FALSE.

Syntax

(next handlerp)

12.16.2.2 Calling Shadowed Handlers

If the conditions are such that the function next handlerp would return the symbol TRUE, then calling this function will execute the shadowed method. Otherwise, a message execution error (see section 9.5.4) will occur. In the event of an error, the return value of this function is the symbol FALSE, otherwise it is the return value of the shadowed handler. The shadowed handler is passed the same arguments as the calling handler.


A handler may continue execution after calling call next handler. In addition, a handler may make multiple calls to call next handler, and the same shadowed handler will be executed each time.

Syntax

(call next handler)

Example

CLIPS> (clear)

CLIPS> (defclass A (is-a USER) (role concrete))

CLIPS>

(defmessage-handler A print-args ($?any)

(printout t “A: ” ?any crlf)

(if (next-handlerp) then

(call-next-handler)))

CLIPS>

(defmessage-handler USER print-args ($?any)

(printout t “USER: ” ?any crlf))

CLIPS> (make-instance a of A)

[a]

CLIPS> (send [a] print-args 1 2 3 4)

A: (1 2 3 4)

USER: (1 2 3 4)

CLIPS>

12.16.2.3 Calling Shadowed Handlers with Different Arguments

This function is identical to call next handler except that this function can change the arguments passed to the shadowed handler.

Syntax

(override next handler <expression>*)

Example

CLIPS> (clear)

CLIPS> (defclass A (is-a USER) (role concrete))

CLIPS>

(defmessage-handler A print-args ($?any)

(printout t “A: ” ?any crlf)

(if (next-handlerp) then

(override-next-handler (rest$ ?any))))

CLIPS>

(defmessage-handler USER print-args ($?any)

(printout t “USER: ” ?any crlf))

CLIPS> (make-instance a of A)

[a]

CLIPS> (send [a] print-args 1 2 3 4)

A: (1 2 3 4)

USER: (2 3 4)

CLIPS>

12.16.3 Definstances Functions

12.16.3.1 Getting the List of Definstances

The function get definstances list returns a multifield value containing the names of all definstances constructs visible to the module specified by <module-name> or to the current module if none is specified. If * is specified as the module name, then all definstances are returned.

Syntax

(get definstances list [<module-name>])

Example

CLIPS> (clear)

CLIPS> (get-definstances-list)

()

CLIPS> (definstances foo)

CLIPS> (definstances bar)

CLIPS> (get-definstances-list)

(foo bar)

CLIPS>

12.16.3.2 Determining the Module in which a Definstances is Defined

This function returns the module in which the specified definstances name is defined.

Syntax

(definstances module <definstances-name>)

12.16.4 Instance Manipulation Functions and Actions

12.16.4.1 Initializing an Instance

This function implements the init message handler attached to the class USER (see section 9.4.5.1). This function evaluates and places slot expressions given by the class definition that were not specified by slot overrides in the call to make instanceor initialize instance (see section 9.6.1). This function should never be called directly unless an init message handler is being defined such that the one attached to USER will never be called. However, such a definition is unusual and recommended only to advanced users. A user defined class which does not inherit indirectly or directly from the class USER will require an init message handler which calls this function in order for instances of the class to be created. If this function is called from an init message within the context of a make instance or initialize instance call and there are no errors in evaluating the class defaults, this function will return the address of the instance it is initializing. Otherwise, this function will return the symbol FALSE.

Syntax

(init slots)

12.16.4.2 Deleting an Instance

This function deletes the specified instances by sending them a delete message. The argument can be one or more instance names, instance addresses, or symbols (an instance name without enclosing brackets). The instance specified by the arguments must exist (except in the case of “*”). If “*” is specified for the instance, all instances will be sent the delete message (unless there is an instance named “*”). This function returns the symbol TRUE if all instances were successfully deleted, otherwise it returns the symbol FALSE. Note, this function is exactly equivalent to sending the instance(s) the delete message directly and is provided only as an intuitive counterpart to the function retract for facts.

Syntax

(unmake instance <instance-expression>+)

12.16.4.3 Deleting the Active Instance from a Handler

This function operates implicitly on the active instance (see section 9.4.1.1) for a message, and thus can only be called from within the body of a message handler. This function directly deletes the active instance and is the one used to implement the delete handler attached to class USER (see section 9.4.5.2). This function returns the symbol TRUE if the instance was successfully deleted, otherwise the symbol FALSE.

Syntax

(delete instance)

12.16.4.4 Determining the Class of an Object

This function returns a symbol which is the name of the class of its argument. It returns the symbol FALSE on errors. This function is equivalent to the type function (see section 12.15.4).

Syntax

(class <object-expression>)

Example

CLIPS> (class 34)

INTEGER

CLIPS>

12.16.4.5 Determining the Name of an Instance

This function returns a symbol which is the name of its instance argument. It returns the symbol FALSE on errors. The evaluation of the argument must be an instance name or instance address of an existing instance.

Syntax

(instance name <instance-expression>)

12.16.4.6 Determining the Address of an Instance

This function returns the address of its instance argument. It returns the symbol FALSE on errors. The evaluation of <instance expression> must be an instance name or instance address of an existing instance. If <module> or * is not specified, the function searches only in the current module. If * is specified, the current module and imported modules are recursively searched. If <module> is specified, only that module is searched. The :: syntax cannot be used with the instance name if <module> or * is specified.

Syntax

(instance address [<module> | *] <instance-expression>)

12.16.4.7 Converting a Symbol to an Instance Name

This function returns an instance name which is equivalent to its symbol argument. It returns the symbol FALSE on errors.

Syntax

(symbol to instance name <symbol-expression>)

Example

CLIPS> (symbol-to-instance-name (sym-cat abc def))

[abcdef]

CLIPS>

12.16.4.8 Converting an Instance Name to a Symbol

This function returns a symbol which is equivalent to its instance name argument. It returns the symbol FALSE on errors.

Syntax

(instance name to symbol <instance-name-expression>)

Example

CLIPS> (instance-name-to-symbol [a])

a

CLIPS>

12.16.4.9 Predicate Functions

12.16.4.9.1 Testing for an Instance


This function returns the symbol TRUE if the evaluation of its argument is an instance address or an instance name. Otherwise, it returns the symbol FALSE.

Syntax

(instancep <expression>)

12.16.4.9.2 Testing for an Instance Address

This function returns the symbol TRUE if the evaluation of its argument is an instance address. Otherwise, it returns the symbol FALSE.

Syntax

(instance addressp <expression>)

12.16.4.9.3 Testing for an Instance Name

This function returns the symbol TRUE if the evaluation of its argument is an instance name. Otherwise, it returns the symbol FALSE.

Syntax

(instance namep <expression>)

12.16.4.9.4 Testing for the Existence an Instance

This function returns the symbol TRUE if the specified instance exists. Otherwise, it returns the symbol FALSE. If the argument is an instance name, the function determines if an instance of the specified name exists. If the argument is an instance address, the function determines if the specified address is still valid.

Syntax

(instance existp <instance-expression>)

12.16.4.10 Reading a Slot Value

This function returns the value of the specified slot of the active instance (see section 9.4.1.1). If the slot does not exist, the slot does not have a value or this function is called from outside a message handler, this function will return the symbol FALSE and an error will be generated. This function differs from the ?self:<slot name> syntax in that the slot is not looked up until the function is actually called. Thus it is possible to access different slots every time the function is executed (see section 9.4.2 for more detail). This function bypasses message passing.

Syntax

(dynamic get <slot-name-expression>)

12.16.4.11 Setting a Slot Value

This function sets the value of the specified slot of the active instance (see section 9.4.1.1). If the slot does not exist, there is an error in evaluating the arguments to be placed or this function is called from outside a message handler, this function will return the symbol FALSE and an error will be generated. Otherwise, the new slot value is returned. This function differs from the (bind ?self:<slot name> <value>*) syntax in that the slot is not looked up until the function is actually called. Thus it is possible to access different slots every time the function is executed (see section 9.4.2 for more detail). This function bypasses message passing.

Syntax

(dynamic put <slot-name-expression> <expression>*)

12.16.4.12 Multifield Slot Functions

The following functions allow convenient manipulation of multifield slots. There are three types of functions: replacing a range of fields with one or more new values, inserting one or more new values at an arbitrary point, and deleting a range of fields. For each type, there are two forms of functions: an external interface which sets the new value for the multifield slot with a put  message (see section 9.3.3.9), and an internal interface that can only be called from message handlers which sets the slot for the active instance (see section 9.4.1.1) directly. Both forms read the original value of the slot directly without the use of a get  message. All of these functions return the new slot value on success and the symbol FALSE on errors.

12.16.4.12.1 Replacing Fields

Allows the replacement of a range of fields in a multifield slot value with one or more new values. The range indices must be from 1..n, where n is the number of fields in the multifield slot’s original value and n > 0.

External Interface Syntax

(slot replace$ <instance-expression> <mv-slot-name>

<range-begin> <range-end> <expression>+)

Internal Interface Syntax

(slot-direct replace$ <mv-slot-name>

<range-begin> <range-end> <expression>+)

Example

CLIPS>

(defclass A (is-a USER)

(role concrete)

(multislot mfs (default a b c d e)

(create-accessor write)))

CLIPS> (make-instance a of A)

[a]

CLIPS> (slot-replace$ a mfs 2 4 2 3 4)

(a 2 3 4 e)

CLIPS>

12.16.4.12.2 Inserting Fields

Allows the insertion of one or more new values in a multifield slot value before a specified field index. The index must greater than or equal to 1. A value of 1 inserts the new value(s) at the beginning of the slot’s value. Any value greater than the length of the slot’s value appends the new values to the end of the slot’s value.

External Interface Syntax

(slot insert$ <instance-expression> <mv-slot-name>

<index> <expression>+)

Internal Interface Syntax

(slot-direct insert$ <mv-slot-name> <index> <expression>+)

Example

CLIPS> (initialize-instance a)

[a]

CLIPS> (slot-insert$ a mfs 2 4 2 3 4)

(a 4 2 3 4 b c d e)

CLIPS>

12.16.4.12.3 Deleting Fields

Allows the deletion of a range of fields in a multifield slot value. The range indices must be from 1..n, where n is the number of fields in the multifield slot’s original value and n > 0.

External Interface Syntax

(slot delete$ <instance-expression> <mv-slot-name>

<range-begin> <range-end>)

Internal Interface Syntax

(slot-direct delete$ <mv-slot-name> <range-begin> <range-end>)

Example

CLIPS> (initialize-instance a)

[a]

CLIPS> (slot-delete$ a mfs 2 4)

(a e)

CLIPS>

12.17 Defmodule Functions

The following functions provide ancillary capabilities for the defmodule construct.

12.17.1 Getting the List of Defmodules

The function get defmodule list returns a multifield value containing the names of all defmodules that are currently defined.

Syntax

(get defmodule list)

Example

CLIPS> (clear)

CLIPS> (get-defmodule-list)

(MAIN)

CLIPS> (defmodule A)

CLIPS> (defmodule B)

CLIPS> (get-defmodule-list)

(MAIN A B)

CLIPS>

12.17.2 Setting the Current Module

This function sets the current module. It returns the name of the previous current module. If an invalid module name is given, then the current module is not changed and the name of the current module is returned.

Syntax

(set current module <defmodule-name>)

12.17.3 Getting the Current Module

This function returns the name of the current module.

Syntax

(get current module)

12.18 Sequence Expansion

In the past, there has been no distinction between single field and multifield variable references within function calls (as opposed to declaring variables for function parameters or variables used for pattern matching). For example, for the rule:

(defrule expansion

(foo $?b)

(printout t ?b crlf)

(printout t $?b crlf))


would have given identical output for both printout statements in version 5.1 of CLIPS.


CLIPS> (assert (foo a b c))

<Fact-0>

CLIPS> (run)

(a b c)

(a b c)

CLIPS>


Multifield variable references within function calls are now treated differently. The $ acts as a “sequence expansion” operator and has special meaning when applied to a global or local variable reference within the argument list of a function call. The $ means to take the fields of the multifield value referenced by the variable and treat them as separate arguments to the function as opposed to passing a single multifield value argument.


For example, using sequence expansion with the expansion rule would give the following output:


CLIPS> (assert (foo a b c))

<Fact-0>

CLIPS> (run)

(a b c)

abc

CLIPS>


Using sequence expansion, the two printout statements on the RHS of the expansion rule are equivalent to:


(printout t (create$ a b c) crlf)

(printout t a b c crlf)


The $ operator also works with global variables. For example:

CLIPS> (defglobal ?*x* = (create$ 3 4 5))

CLIPS> (+ ?*x*)

ERROR: Function + expected at least 2 argument(s)

CLIPS> (+ $?*x*)

12

CLIPS>


The sequence expansion operator is particularly useful for generic function methods. Consider the ease now of defining a general addition function for strings.


(defmethod + (($?any STRING))

(str-cat $?any))


By default, sequence expansion is disabled. This allows previously existing CLIPS programs to work correctly with version 6.0 of CLIPS. The behavior can be enabled using the set sequence operator recognition function described in section 12.18.3. Old CLIPS code should be changed so that it works properly with sequence expansion enabled.

12.18.1 Sequence Expansion and Rules

Sequence expansion is allowed on the LHS of rules, but only within function calls. If a variable is specified in a pattern as a single or multifield variable, then all other references to that variable that are not within function calls must also be the same. For example, the following rule is not allowed


(defrule bad-rule-1

(pattern $?x ?x $?x)

⇒)


The following rules illustrate appropriate use of sequence expansion on the LHS of rules.


(defrule good-rule-1

(pattern $?x&:(> (length$ ?x) 1))

(another-pattern $?y&:(> (length$ ?y) 1))

(test (> (+ $?x) (+ $?y)))

⇒)


The first and second patterns use the length$ function to determine that the multifields bound to ?x and ?y are greater than 1. Sequence expansion is not used to pass ?x and ?y to the length$ function since the length$ function expects a single argument of type multifield. The test CE calls the + function to determine the sum of the values bound to ?x and ?y. Sequence expansion is used for these function calls since the + function expects two or more arguments with numeric data values.


Sequence expansion has no affect within an assert, modify, or duplicate; however, it can be used with other functions on the RHS of a rule.

12.18.2 Multifield Expansion Function

The $ operator is merely a shorthand notation for the expand$ function call. For example, the function calls


(printout t $?b crlf)


and


(printout t (expand$ ?b) crlf)


are identical.

Syntax

(expand$ <multifield-expression>)


The expand$ function is valid only within the argument list of a function call. The expand$ function (and hence sequence expansion) cannot be used as an argument to the following functions: expand$, return, progn, while, if, progn$, switch, loop for count, assert, modify, duplicate and object pattern match delay.

12.18.3 Setting The Sequence Operator Recognition Behavior

This function sets the sequence operator recognition behavior. When this behavior is disabled (FALSE by default), multifield variables found in function calls are treated as a single argument. When this behaviour is enabled, multifield variables are expanded and passed as separate arguments in the function call. This behavior should be set before an expression references a multifield variable is encountered (i.e. changing the behavior does not retroactively change the behavior for previously encountered expressions). The return value for this function is the old value for the behavior.

Syntax

(set sequence operator recognition <boolean-expression>)

12.18.4 Getting The Sequence Operator Recognition Behavior

This function returns the current value of the sequence operator recognition behavior (TRUE or FALSE).

Syntax

(get sequence operator recognition)

12.18.5 Sequence Operator Caveat

CLIPS normally tries to detect as many constraint errors as possible for a function call at parse time, such as bad number of arguments or types. However, if the sequence expansion operator is used in the function call, all such checking is delayed until run time (because the number and types of arguments can change for each execution of the call.) For example:


CLIPS> (deffunction foo (?a ?b))

CLIPS> (deffunction bar ($?a) (foo ?a))

ERROR: Function foo expected exactly 2 argument(s)


ERROR:

(deffunction bar

($?a)

(foo ?a)

CLIPS> (deffunction bar ($?a) (foo $?a))

CLIPS> (bar 1)

ERROR: Function foo expected exactly 2 argument(s)

FALSE

CLIPS> (bar 1 2)

FALSE

CLIPS>

Section 13   Commands

This section describes commands primarily intended for use from the top level command prompt. These commands may also be used from constructs and other places where functions can be used.

13.1 Environment Commands

The following commands control the CLIPS environment.

13.1.1 Loading Constructs From A File

.Loads the constructs stored in the file specified by <file name> into the environment. If the compilations item is being watched (see section 13.2), then an informational message (including the type and name of the construct) will be displayed for each construct loaded. If the compilations item is not being watched, then a character is printed for each construct loaded (“*” for defrule, “$” for deffacts, “%” for deftemplate, “:” for defglobal, “!” for deffunction, “^” for defgeneric, “&” for defmethod, “#” for defclass, “~” for defmessage handler, “@” for definstances, and “+” for defmodule). This function returns TRUE if the file was successfully loaded, otherwise FALSE is returned.

Syntax

(load <file-name>)

13.1.2 Loading Constructs From A File without Progress Information

Loads the constructs stored in the file specified by <file name> into the environment, however, unlike the load command informational messsages are not printed to show the progress of loading the file. Error messages are still printed if errors are encountered while loading the file. This function returns TRUE if the file was successfully loaded, otherwise FALSE is returned.

Syntax

(load* <file-name>)

13.1.3 Saving All Constructs To A File

Saves all of the constructs (defrules, deffacts, deftemplates, etc.) in the current envi­ronment into the file specified by <file name>. Note that deffunctions and generic functions are saved twice to the file. Because it is possible to create circular references among deffunctions and generic functions by redefining them, a forward declaration (containing no actions) of the functions is saved first to the file, and then the actual declaration (containing the actions) is saved. This function returns TRUE if the file was successfully saved, otherwise FALSE is returned. This function uses the pretty print forms of the constructs. If pretty printing has been disabled by the conserve mem command, then the save command will have no output.

Syntax

(save <file-name>)

13.1.4 Loading a Binary Image

Loads the constructs stored in the binary file specified by <file name> into the environment. The specified file must have been created by bsave. Loading a binary image is quicker than using the load command to load a ASCII text file. A bload clears all constructs from the current CLIPS environment (as well as all facts and instances). Bload can be called at any time unless some constructs that bload will affect are in use (e.g. a deffunction is currently executing). The only constructive/destructive operation that can occur after a bload is the clear command or the bload command (which clears the current binary image). This means that constructs cannot be loaded or deleted while a bload is in effect. In order to add constructs to a binary image, the original ASCII text file must be reloaded, the new constructs added, and then another bsave must be performed. This function returns TRUE if the file was successfully bloaded, otherwise FALSE is returned.


Binary images can be loaded into different compile time configurations of CLIPS, as long as the same version of CLIPS is used and all the functions and constructs needed by the binary image are supported. In addition, binary images should theoretically work across different hardware platforms if internal data representations are equivalent (e.g. same integer size, same byte order, same floating point format, etc). However, it is NOT recommended that this be attempted.

Syntax

(bload <file-name>)

13.1.5 Saving a Binary Image

Saves all of the constructs in the current envi­ronment into the file specified by <file name>. The save file is written using a binary format which results in faster load time. The save file must be loaded via the bload command. A bsave may be performed at any time (except when a bload is in effect). The pretty print representation of a construct is not saved with a binary image (thus, commands like ppdefrule will show no output for any of the rules associated with the binary image). In addition, constraint information associated with constructs is not saved to the binary image unless dynamic constraint checking is enabled (using the set dynamic constraint checking command). This function returns TRUE if the file was successfully bsaved, otherwise FALSE is returned.

Syntax

(bsave <file-name>)

13.1.6 Clearing CLIPS

Clears CLIPS. Removes all constructs and all associated data structures (such as facts and instances) from the CLIPS environment. A clear may be performed safely at any time, however, certain constructs will not allow themselves to be deleted while they are in use. For example, while deffacts are being reset (by the reset command), it is not possible to remove them using the clear command. Note that the clear command does not effect many environment characteristics (such as the current conflict resolution strategy). This function has no return value.

Syntax

(clear)

13.1.7 Exiting CLIPS

Quits CLIPS. This function has no return value.

Syntax

(exit [<integer-expression>])


The optional <integer-expression> argument allows the exit status code to be specified which is eventually passed to the C exit function.

13.1.8 Resetting CLIPS

Resets CLIPS. Removes all activations from the agenda, all facts from the fact list and all instances of user defined classes, then assigns global variables their initial values, asserts all facts listed in def­facts statements into the fact list, creates all instances listed in definstances statements, sets the current module to the MAIN module and automatically focuses on the same module. Incremental reset is supported for rules. This means that rules can be activated from facts that were asserted before the rule was defined without performing a reset. A reset can be performed while rules are executing. Note that the reset command does not effect many environment characteristics (such as the current conflict resolution strategy). This function has no return value.

Syntax

(reset)

13.1.9 Executing Commands From a File

Allows “batch” processing of CLIPS interactive com­mands by replacing standard input with the contents of a file. Any command or function can be used in a batch file, as well as construct definitions and re­sponses to read or readline function calls. The load command should be used in batch files rather than defining constructs directly. The load command expects only constructs and hence moves to the next construct when an error occurs. The batch command, however, moves on until it finds the next construct or command (and in the case of a construct this is likely to generate more errors as the remaining commands and functions in the construct are parsed). This function returns TRUE if the batch file was successfully executed, otherwise FALSE is returned. Note that the batch command operates by replacing standard input rather than by immediately executing the commands found in the batch file. In effect, if you execute a batch command from the RHS of a rule, the commands in that batch file will not be processed until control is returned to the top level prompt.

Syntax

(batch <file-name>)


13.1.10 Executing Commands From a File Without Replacing Standard Input

Evaluates the series of commands stored in the file specified by <file name>. Unlike the batch command, batch* evaluates all of the commands in the specified file before returning. The batch* command does not replace standard input and thus a batch* file cannot be used to provide input to functions such as read and readline. In addition, commands stored in the batch* file and the return value of these commands are not echoed to standard output.


The batch* command is not available for binary-load only or run time CLIPS configurations (see the Advanced Programming Guide).

Syntax

(batch* <file-name>)

13.1.11 Determining CLIPS Compilation Options

Generates a textual description of the settings of the CLIPS compiler flags. This function has no return value.

Syntax

(options)

13.1.12 Calling the Operating System

The system function allows a call to the operating system. It is patterned after the system function provided to C on most UNIX systems. This function has no return value.

Syntax

(system <lexeme-expression>*)

Example

(defrule print-directory
(print-directory ?directory)

(system “dir ” ?directory)); Note space ⇒ “dir<space>”


Note that any spaces needed for a proper parsing of the system command must be added by the user in the call to system. Also note that the system command is not guaranteed to execute (e.g., the operating system may not have enough memory to spawn a new process).


Portability Note

Not all operating systems/compilers provide this function. The code is stored in the sysdep.c file, and the default coding for generic CLIPS is a non­functional stub that will compile on any machine. On some machines (such as an IBM PC running DOS), there may be insufficient memory available to spawn a subprocess to execute the system command. In such a case, the command will not be executed and the system command will return with no action taken.

13.1.13 Setting The Auto Float Dividend Behavior

This function sets auto float dividend behavior. When this behavior is enabled (TRUE by default) the dividend of the division function is automatically converted to a floating point number. The return value for this function is the old value for the behavior.

Syntax

(set auto float dividend <boolean-expression>)

13.1.14 Getting The Auto Float Dividend Behavior

This function returns the current value of the auto float dividend behavior (TRUE or FALSE).

Syntax

(get auto float dividend)

13.1.15 Setting the Dynamic Constraint Checking Behavior

This function sets dynamic constraint checking behavior. When this behavior is disabled (FALSE by default), newly created data objects (such as deftemplate facts and instances) do not have their slot values checked for constraint violations. When this behavior is enabled (TRUE), the slot values are checked for constraint violations. The return value for this function is the old value for the behavior. Constraint information is not saved when using the bload and constructs to c command if dynamic constraint checking is disabled.

Syntax

(set dynamic constraint checking <boolean-expression>)

13.1.16 Getting the Dynamic Constraint Checking Behavior

This function returns the current value of the dynamic constraint checking behavior (TRUE or FALSE).

Syntax

(get dynamic constraint checking)

13.1.17 Setting the Static Constraint Checking Behavior

This function sets static constraint checking behavior. When this behavior is disabled (FALSE), constraint violations are not checked when function calls and constructs are parsed. When this behavior is enabled (TRUE by default), constraint violations are checked when function calls and constructs are parsed. The return value for this function is the old value for the behavior.

Syntax

(set static constraint checking <boolean-expression>)

13.1.18 Getting the Static Constraint Checking Behavior

This function returns the current value of the static constraint checking behavior (TRUE or FALSE).

Syntax

(get static constraint checking)

13.1.19 Finding Symbols

This command displays all symbols currently defined in CLIPS which contain a specified substring. This command has no return value.

Syntax

(apropos <lexeme>)

Example

CLIPS> (apropos pen)

dependents

mv-append

open

dependencies

CLIPS>


Portability Note

If the ANSI_COMPILER flag has been set to 0, then apropos only shows those symbols that begin with the specified substring.

13.2 Debugging Commands

The following commands control the CLIPS debugging features.

13.2.1 Generating Trace Files

Sends all information normally sent to the logical names wclips,wdialog, wdisplay, werror, wwarning,wtrace, and stdout to <file name> as well as to their normal destination. Additionally, all information received from logical name stdin is also sent to <file name> as well as being returned by the requesting function. This function returns TRUE if the dribble file was successfully opened, otherwise FALSE is returned.

Syntax

(dribble on <file-name>)

13.2.2 Closing Trace Files

Stops sending trace information to the dribble file. This function returns TRUE if the dribble file was successfully closed, otherwise FALSE is returned.

Syntax

(dribble off)

13.2.3 Enabling Watch Items

This function causes messages to be displayed when certain CLIPS operations take place.

Syntax

(watch <watch-item>)


<watch-item> ::= all |

compilations |

statistics |

focus |

messages |

deffunctions <deffunction-name>* |

globals <global-name>* |

rules <rule-name>* |

activations <rule-name>* |

facts <deftemplate-name>* |

instances <class-name>* |

slots <class-name>* |

message-handlers <handler-spec-1>*

[<handler-spec-2>]) |

generic-functions <generic-name>* |

methods <method-spec-1>* [<method-spec-2>]


<handler-spec-1> ::= <class-name>

<handler-name> <handler-type>

<handler-spec-2> ::= <class-name>

[<handler-name> [<handler-type>]]


<method-spec-1> ::= <generic-name> <method-index>

<method-spec-2> ::= <generic-name> [<method-index>]


If compilations are watched, the progress of construct definitions will be displayed.


If facts are watched, all fact assertions and retractions will be displayed. Optionally, facts associated with individual deftemplates can be watched by specifying one or more deftemplate names.


If rules are watched, all rule firings will be dis­played. If activations are watched, all rule activations and deactivations will be displayed. Optionally, rule firings and activations associated with individual defrules can be watched by specifying one or more defrule names. If statistics are watched, timing information along with other information (average number of facts, average number of activations, etc.) will be displayed after a run. Note that the number of rules fired and timing information is not printed unless this item is being watch. If focus is watched, then changes to the current focus will be displayed.


If globals are watched, variable assignments to globals variables will be displayed. Optionally, variable assignments associated with individual defglobals can be watched by specifying one or more defglobal names. If deffunctions are watched, the start and finish of deffunctions will be displayed. Optionally, the start and end display associated with individual deffunctions can be watched by specifying one or more deffunction names.


If generic functions are watched, the start and finish of generic functions will be displayed. Optionally, the start and end display associated with individual defgenerics can be watched by specifying one or more defgeneric names. If methods are watched, the start and finish of individual methods within a generic function will be displayed. Optionally, individual methods can be watched by specifying one or more methods using a defgeneric name and a method index. When the method index is not specified, then all methods of the specified defgeneric will be watched.


If instances are watched, creation and deletion of instances will be displayed. If slots are watched, changes to any instance slot values will be displayed. Optionally, instances and slots associated with individual concrete defclasses can be watched by specifying one or more concrete defclass names. If message handlers are watched, the start and finish of individual message handlers within a message will be displayed. Optionally, individual message handlers can be watched by specifying one or more message handlers using a defclass name, a message handler name, and a message handler type. When the message handler name and message handler type are not specified, then all message handlers for the specified class will be watched. When the message handler type is not specified, then all message handlers for the specified class with the specified message handler name will be watched. If messages are watched, the start and finish of messages will be displayed.


For the watch items that allow individual constructs to be watched, if no constructs are specified, then all constructs of that type will be watched. If all constructs associated with a watch item are being watched, then newly defined constructs of the same type will also be watched. A construct retains its old watch state if it is redefined. If all is watched, then all other watch items will be watched. By default, only compilations are watched. The watch function has no return value.

Example

CLIPS> (watch rules)

CLIPS>

13.2.4 Disabling Watch Items

This function disables the effect of the watch command.

Syntax

(unwatch watch-item>)


This command is identical to the watch command with the exception that it disables watch items rather than enabling them. This function has no return value.

Example

CLIPS> (unwatch all)

CLIPS>

13.2.5 Viewing the Current State of Watch Items

This command displays the current state of watch items.

Syntax

(list watch items [<watch-item>])


This command displays the current state of all watch items. If called without the <watch item> argument, the global watch state of all watch items is displayed. If called with the <watch item> argument, the global watch state for that item is displayed followed by the individual watch states for each item of the specified type which can be watched. This function has no return value.

Example

CLIPS> (list-watch-items)

facts = off

instances = off

slots = off

rules = off

activations = off

messages = off

message-handlers = off

generic-functions = off

methods = off

deffunctions = off

compilations = on

statistics = off

globals = off

focus = off

CLIPS> (list-watch-items facts)

facts = off

MAIN:

initial-fact = off

CLIPS>

13.3 Deftemplate Commands

The following commands manipulate deftemplates.

13.3.1 Displaying the Text of a Deftemplate

Displays the text of a given deftemplate. This function has no return value.

Syntax

(ppdeftemplate <deftemplate-name>)

13.3.2 Displaying the List of Deftemplates

Displays the names of all deftemplates. This function has no return value.

Syntax

(list deftemplates [<module-name>])


If <module name> is unspecified, then the names of all deftemplates in the current module are displayed. If <module name> is specified, then the names of all deftemplates in the specified module are displayed. If <module name> is the symbol *, then the names of all deftemplates in all modules are displayed.

13.3.3 Deleting a Deftemplate

This function deletes a previously defined deftemplate.

Syntax

(undeftemplate <deftemplate-name>)


If the deftemplate is in use (for example by a fact or a rule), then the deletion will fail. Otherwise, no further uses of the deleted deftemplate are permitted (unless redefined). If the symbol * is used for <deftemplate name>, then all deftemplates will be deleted (unless there is a deftemplate named *). This function has no return value.

13.4 Fact Commands

The following commands display information about facts.

13.4.1 Displaying the Fact-List

Displays facts stored in the fact list.

Syntax

(facts [<module-name>]

[<start-integer-expression>

[<end-integer-expression>

[<max-integer-expression>]]])


If <module name> is not specified, then only facts visible to the current module will be displayed. If <module name> is specified, then only facts visible to the specified module are displayed. If the symbol * is used for <module name>, then facts from any module may be displayed. If the start argument is speci­fied, only facts with fact indices greater than or equal to this argument are displayed. If the end argument is speci­fied, only facts with fact indices less than or equal to this argument are displayed. If the max argument is speci­fied, then no facts will be displayed beyond the specified maximum number of facts to be displayed. This function has no return value.

13.4.2 Loading Facts From a File

This function will assert a file of information as facts into the CLIPS fact list. It can read files created with save facts or any ASCII text file. Each fact should begin with a left parenthesis and end with a right parenthesis. Facts may span across lines and can be written in either ordered or deftemplate format. This function returns TRUE if the fact file was successfully loaded, otherwise FALSE is returned.

Syntax

(load facts <file-name>)

13.4.3 Saving The Fact-List To A File

This function saves all of the facts in the current fact list into the file specified by <file name>. External address and fact address fields are saved as strings. Instance address fields are converted to instance names. Optionally, the scope of facts to be saved can be specified. If <save scope> is the symbol visible, then all facts visible to the current module are saved. If <save scope> is the symbol local, then only those facts with deftemplates defined in the current module are saved. If <save scope> is not specified, it defaults to local. If <save scope> is specified, then one or more deftemplate names may also be specified. In this event, only those facts with associated with a corresponding deftemplate in the specified list will be saved. This function returns TRUE if the fact file was successfully saved, otherwise FALSE is returned.

Syntax

(save facts <file-name> [<save-scope> <deftemplate-names>*])

<save-scope> ::= visible | local

13.4.4 Setting the Duplication Behavior of Facts

This function sets fact duplication behavior. When this behavior is disabled (FALSE by default), asserting a duplicate of a fact already in the fact list produces no effect. When enabled (TRUE), the duplicate fact is asserted with a new fact index. The return value for this function is the old value for the behavior.

Syntax

(set fact duplication <boolean-expression>)


Example

CLIPS> (get-fact-duplication)

FALSE

CLIPS> (watch all)

CLIPS> (assert (a))

==> f-0 (a)

<Fact-0>

CLIPS> (assert (a))

FALSE

CLIPS> (set-fact-duplication TRUE)

FALSE

CLIPS> (assert (a))

==> f-1 (a)

<Fact-1>

CLIPS>

13.4.5 Getting the Duplication Behavior of Facts

This function returns the current value of the fact duplication behavior (TRUE or FALSE).

Syntax

(get fact duplication)


13.5 Deffacts Commands

The following commands manipulate deffacts.

13.5.1 Displaying the Text of a Deffacts

Displays the text of a given deffacts. This function has no return value.

Syntax

(ppdeffacts <deffacts-name>)

13.5.2 Displaying the List of Deffacts

Displays the names of all deffacts stored in the CLIPS environment.

Syntax

(list deffacts [<module-name>])


If <module name> is unspecified, then the names of all deffacts in the current module are displayed. If <module name> is specified, then the names of all deffacts in the specified module are displayed. If <module name> is the symbol *, then the names of all deffacts in all modules are displayed. This function has no return value.

13.5.3 Deleting a Deffacts

This function deletes a previously defined deffacts.

Syntax

(undeffacts <deffacts-name>)


All facts listed in the deleted deffacts construct will no longer be asserted as part of a reset. If the symbol * is used for <deffacts name>, then all deffacts will be deleted (unless there exists a deffacts named *). The undeffacts command can be used to remove deffacts at any time. Exceptions: When deffacts are being reset as part of the reset command, they cannot be removed. This function has no return value.

13.6 Defrule Commands

The following commands manipulate defrules.

13.6.1 Displaying the Text of a Rule

Displays the text of a given rule.

Syntax

(ppdefrule <rule-name>)


The pprule command can also be used for this purpose. This function has no return value.

13.6.2 Displaying the List of Rules

Displays the names of all rules stored in the CLIPS environment.

Syntax

(list defrules [<module-name>])


If <module name> is unspecified, then the names of all defrules in the current module are displayed. If <module name> is specified, then the names of all defrules in the specified module are displayed. If <module name> is the symbol *, then the names of all defrules in all modules are displayed. This function has no return value.

13.6.3 Deleting a Defrule

This function deletes a previously defined defrule.

Syntax

(undefrule <defrule-name>)


If the defrule is in use (for example if it is firing), then the deletion will fail. If the symbol * is used for <defrule name>, then all defrule will be deleted (unless there is a defrule named *). This function has no return value.

13.6.4 Displaying Matches for a Rule

For a specified rule, displays the list of the facts or instances which match each pattern in the rule’s LHS, the partial matches for the rule, and the activations for the rule. Note that the patterns for which information is displayed include the patterns added or rearranged by CLIPS (see section 5.4.9). When listed as a partial match, the not, exists, and forall CEs are shown as a comma with no following pattern entity identifier (such as a fact-index or instance name). Other CEs contained within these CEs are not displayed as part of the information shown for a partial match. This function has no return value.

Syntax

(matches <rule-name>)

Example

The rule matches-example-1 has three patterns and none are added by CLIPS. Fact f-1 matches the first pattern, facts f-2 and f-3 match the the second pattern, and fact f-4 matches the third pattern. Issuing the run command will remove all of the rule’s activations from the agenda.


CLIPS> (clear)

CLIPS>

(defrule matches-example-1

(a ?)

(b ?)

(c ?)

⇒)

CLIPS> (reset)

CLIPS> (assert (a 1) (b 1) (b 2) (c 1))

<Fact-4>

CLIPS> (facts)

f-0 (initial-fact)

f-1 (a 1)

f-2 (b 1)

f-3 (b 2)

f-4 (c 1)

For a total of 5 facts.

CLIPS> (run)

CLIPS>


The rule matches-example-2has four patterns of which one was added by CLIPS (the initial-fact pattern is added to the very beginning of the rule). The initial-fact, f-0, matches the first pattern, there are no matches for the second pattern (since there are no d facts), facts f-2 and f-3 match the third pattern, and fact f-4 matches the forth pattern.



CLIPS>

(defrule matches-example-2

(not (d ?))

(exists (b ?x)

(c ?x))

⇒)

CLIPS>


Listing the matches for the rule matches-example-1 displays the matches for the patterns indicated previously. There are two partial matches which satisfy the first two patterns and two partial matches which satisfy all three patterns. Since all of the rule’s activations were allowed to fire there are none listed.


CLIPS> (matches matches-example-1)

Matches for Pattern 1

f-1

Matches for Pattern 2

f-2

f-3

Matches for Pattern 3

f-4

Partial matches for CEs 1 - 2

f-1,f-3

f-1,f-2

Partial matches for CEs 1 - 3

f-1,f-2,f-4

f-1,f-3,f-4

Activations

None

CLIPS>


Listing the matches for the rule matches-example-2 displays the matches for the patterns indicated previously. There is one partial match which satisfies the first two patterns (the initial-fact pattern and the not CE). The match for the second CE is indicated by the comma followed by no additional pattern entity identifier. There is also one partial match which satisfies the first three patterns (the initial-fact pattern, the not CE, and the exists CE). Again, the match for the third CE is indicated by a command followed by no additional pattern entity identifier. Since none of the rule’s activations were allowed to fire they are listed. The list of activations will always be a subset of the partial matches for all of the rule’s CEs.


CLIPS> (matches matches-example-2)

Matches for Pattern 1

f-0

Matches for Pattern 2

None

Matches for Pattern 3

f-2

f-3

Matches for Pattern 4

f-4

Partial matches for CEs 1 - 2

f-0,

Partial matches for CEs 1 - 3

f-0,,

Activations

f-0,,

CLIPS>

13.6.5 Setting a Breakpoint for a Rule

Sets a breakpoint for a given rule.

Syntax

(set break <rule-name>)


If a breakpoint is set for a given rule, execution will stop prior to executing that rule. At least one rule must fire before a break­point will stop execution. This function has no return value.

13.6.6 Removing a Breakpoint for a Rule

Removes a breakpoint for a given rule.

Syntax

(remove break [<defrule-name>])


If no argument is given, then all breakpoints are removed. This function has no return value.

13.6.7 Displaying Rule Breakpoints

This command displays all the rules which have breakpoints set. This function has no return value.

Syntax

(show breaks [<module-name>])


If <module name> is unspecified, then the names of all rules having breakpoints in the current module are displayed. If <module name> is specified, then the names of all rules having breakpoints in the specified module are displayed. If <module name> is the symbol *, then the names of all rules having breakpoints in all modules are displayed.

13.6.8 Refreshing a Rule

Places all current activations of a given rule on the agenda. This function has no return value.

Syntax

(refresh <rule-name>)

13.6.9 Setting the Incremental Reset Behavior

This function sets the incremental reset behavior. When this behavior is enabled (TRUE by default), newly defined rules are updated based upon the current state of the fact list. When disabled (FALSE), newly defined rules are only updated by facts added after the rule is defined. In order to prevent rules from obtaining an inconsistent state, the incremental reset behavior can only be changed when there are no rules currently defined. The return value for this function is the old value for the behavior.

Syntax

(set incremental reset <boolean-expression>)

13.6.10 Getting the Incremental Reset Behavior

This function returns the current value of the incremental reset behavior (TRUE or FALSE).

Syntax

(get incremental reset)

13.6.11 Determining the Logical Dependencies of a Pattern Entity

The dependencies function lists the partial matches from which a pattern entity receives logical support. This function has no return value.

Syntax

(dependencies <fact-or-instance-specifier>)


The term <fact or instance specifier> includes variables bound on the LHS to fact addresses or instance addresses as described in section 5.4.1.8, the fact index of the desired fact (e.g. 3 for the fact labeled f 3), or the instance name (e.g. [object]).

Example

(defrule list-dependencies
?f ← ($?)

(dependencies ?f))

13.6.12 Determining the Logical Dependents of a Pattern Entity

The dependents function lists all pattern entities which receive logical support from a pattern entity. This function has no return value.

Syntax

(dependents <fact-or-instance-specifier>)


The term <fact or instance specifier> includes variables bound on the LHS to fact addresses or instance addresses as described in section 5.4.1.8, the fact index of the desired fact (e.g. 3 for the fact labeled f 3), or the instance name (e.g. [object]).

Example

(defrule list-dependents
?f ← ($?)

(dependents ?f))

13.7 Agenda Commands

The following commands manipulate agenda.

13.7.1 Displaying the Agenda

Displays all activations on the agenda. This function has no return value.

Syntax

(agenda [<module-name>])


If <module name> is unspecified, then all activations in the current module (not the current focus) are displayed. If <module name> is specified, then all activations on the agenda of the specified module are displayed. If <module name> is the symbol *, then the activations on all agendas in all modules are displayed.

13.7.2 Running CLIPS

Starts execution of the rules. If the optional first argument is positive, execu­tion will cease after the specified number of rule firings or when the agenda con­tains no rule activations. If there are no arguments or the first argument is a negative integer, execution will cease when the agenda contains no rule activations. If the focus stack is empty, then the MAIN module is automatically becomes the current focus. The run command has no additional effect if evaluated while rules are executing. Note that the number of rules fired and timing information is no longer printed after the completion of the run command unless the statistics item is being watched (see section 13.2). If the rules item is being watched, then an informational message will be printed each time a rule is fired. This function has no return value.

Syntax

(run [<integer-expression>])

13.7.3 Focusing on a Group of Rules

Pushes one or more modules onto the focus stack. The specified modules are pushed onto the focus stack in the reverse order they are listed. The current module is set to the last module pushed onto the focus stack. The current focus is the top module of the focus stack. Thus (focus A B C) pushes C, then B, then A unto the focus stack so that A is now the current focus. Note that the current focus is different from the current module. Focusing on a module implies “remembering” the current module so that it can be returned to later. Setting the current module with the set current module function changes it without remembering the old module. Before a rule executes, the current module is changed to the module in which the executing rule is defined (the current focus). This function returns a boolean value: FALSE if an error occurs, otherwise TRUE.

Syntax

(focus <module-name>+)

13.7.4 Stopping Rule Execution

The halt function may be used on the RHS of a rule to prevent further rule firing. It is called without arguments. After halt is called, control is returned from the run command. The agenda is left intact, and execution may be continued with a run command. This function has no return value.

Syntax

(halt)

13.7.5 Setting The Current Conflict Resolution Strategy

This function sets the current conflict resolution strategy. The default strategy is depth.

Syntax

(set strategy <strategy>)


where <strategy> is either depth, breadth, simplicity, complexity, lex, mea, or random. The old conflict resolution strategy is returned. The agenda will be reordered to reflect the new conflict resolution strategy.

13.7.6 Getting The Current Conflict Resolution Strategy

This function returns the current conflict resolution strategy (depth, breadth, simplicity, complexity, lex, mea, or random).

Syntax

(get strategy)

13.7.7 Listing the Module Names on the Focus Stack

The command list focus stack list all module names on the focus stack. The first name listed is the current focus.

Syntax

(list focus stack)

13.7.8 Removing all Module Names from the Focus Stack

The command clear focus stack removes all module names from the focus stack.

Syntax

(clear focus stack)

13.7.9 Setting the Salience Evaluation Behavior

This function sets the salience evaluation behavior. By default, salience values are only evaluated when a rule is defined.

Syntax

(set salience evaluation <value>)


where <value> is either when defined, when activated, or every cycle. The return value for this function is the old value for salience evaluation. The value when defined forces salience evaluation at the time of rule definition. The value when activation forces salience evaluation at the time of rule definition and upon being activated. The value every cycle forces evaluation at the time of rule definition, upon being activated, and after every rule firing.

13.7.10 Getting the Salience Evaluation Behavior

This function returns the current salience evaluation behavior (when defined, when activated, or every cycle).

Syntax

(get salience evaluation)

13.7.11 Refreshing the Salience Value of Rules on the Agenda

This function forces reevaluation of saliences of rules on the agenda regardless of the current salience evaluation setting. This function has no return value.

Syntax

(refresh agenda [<module-name>])


If <module name> is unspecified, then the agenda in the current module is refreshed. If <module name> is specified, then the agenda in the specified module is refreshed. If <module name> is the symbol *, then the agenda in every module is refreshed.

13.8 Defglobal Commands

The following commands manipulate defglobals.

13.8.1 Displaying the Text of a Defglobal

Displays the text required to define a given global variable. Note that unlike other constructs such as deffacts and definstances, defglobal definitions have no name associated with the entire construct. The variable name passed to ppdefglobal should not include the question mark or the asterisks (e.g. x is the variable name for the global variable ?*x*). This function has no return value.

Syntax

(ppdefglobal <global-variable-name>)

13.8.2 Displaying the List of Defglobals

Displays the names of all defglobals. This function has no return value.

Syntax

(list defglobals [<module-name>])


If <module name> is unspecified, then the names of all defglobals in the current module are displayed. If <module name> is specified, then the names of all defglobals in the specified module are displayed. If <module name> is the symbol *, then the names of all defglobals in all modules are displayed.

13.8.3 Deleting a Defglobal

This function deletes a previously defined defglobal.

Syntax

(undefglobal <defglobal-name>)


If the defglobal is in use (for example if it is referred to in a deffunction), then the deletion will fail. Otherwise, no further uses of the deleted defglobal are permitted (unless redefined). If the symbol * is used for <defglobal name>, then all defglobals will be deleted (unless there is a defglobal named *). This function has no return value.

13.8.4 Displaying the Values of Global Variables

Displays the names and current values of all defglobals. This function has no return value.

Syntax

(show defglobals [<module-name>])


If <module name> is unspecified, then the names and values of all defglobals in the current module are displayed. If <module name> is specified, then the names and values of all defglobals in the specified module are displayed. If <module name> is the symbol *, then the names and values of all defglobals in all modules are displayed.

13.8.5 Setting the Reset Behavior of Global Variables

This function sets the reset global variables behavior. When this behavior is enabled (TRUE by default) global variables are reset to their original values when the reset command is performed. The return value for this function is the old value for the behavior.

Syntax

(set reset globals <boolean-expression>)

13.8.6 Getting the Reset Behavior of Global Variables

This function returns the current value of the reset global variables behavior (TRUE or FALSE).

Syntax

(get reset globals)

13.9 Deffunction Commands

The following commands manipulate deffunctions.

13.9.1 Displaying the Text of a Deffunction

Displays the text of a given deffunction. This function has no return value.

Syntax

(ppdeffunction <deffunction-name>)

13.9.2 Displaying the List of Deffunctions

Displays the names of all deffunctions stored in the CLIPS environment. This function has no return value.

Syntax

(list deffunctions)

13.9.3 Deleting a Deffunction

This function deletes a previously defined deffunction.

Syntax

(undeffunction <deffunction-name>)


If the symbol * is used for <deffunction name>, then all deffunctions will be deleted (unless there exists a deffunction called *). The undeffunction command can be used to remove deffunctions at any time. Exceptions: A deffunction may not be deleted when it is executing or when there is still a reference to it in another loaded construct, such as a rule RHS. This function has no return value.

13.10 Generic Function Commands

The following commands manipulate generic functions.

13.10.1 Displaying the Text of a Generic Function Header

Displays the text of a given generic function header. This function has no return value.

Syntax

(ppdefgeneric <generic-function-name>)

13.10.2 Displaying the Text of a Generic Function Method

Displays the text of a given method.

Syntax

(ppdefmethod <generic-function-name> <index>)


where <index> is the method index (see section 8.4.2). This function has no return value.

13.10.3 Displaying the List of Generic Functions

Displays the names of all generic functions stored in the CLIPS environment.

Syntax

(list defgenerics [<module-name>])


If <module name> is unspecified, then the names of all defgenerics in the current module are displayed. If <module name> is specified, then the names of all defgenerics in the specified module are displayed. If <module name> is the symbol *, then the names of all defgenerics in all modules are displayed. This function has no return value.

13.10.4 Displaying the List of Methods for a Generic Function

If no name is given, this function lists all generic function methods in the CLIPS environment. If a name is given, then only the methods for the named generic function are listed. The methods are listed in decreasing order of precedence (see section 8.5.2) for each generic function. Method indices can be seen using this function. This function has no return value.

Syntax

(list defmethods [<generic-function-name>])

13.10.5 Deleting a Generic Function

This function deletes a previously defined generic function.

Syntax

(undefgeneric <generic-function-name>)


If the symbol * is used for <generic function name>, then all generic functions will be deleted (unless there exists a generic function called *). This function removes the header and all methods for a generic function. The undefgeneric command can be used to remove generic functions at any time. Exceptions: A generic function may not be deleted when any of its methods are executing or when there is still a reference to it in another loaded construct, such as a rule RHS. This function has no return value.

13.10.6 Deleting a Generic Function Method

This function deletes a previously defined generic function method.

Syntax

(undefmethod <generic-function-name> <index>)


where <index> is the index of the method to be deleted for the generic function. If the symbol * is used for <index>, then all the methods for the generic function will be deleted. (This is different from the undefgeneric command because the header is not removed.) If * is used for <generic function name>, then * must also be specified for <index>, and all the methods for all generic functions will be removed. This function removes the specified method for a generic function, but even if the method removed is the last one, the generic function header is not removed. The undefmethod command can be used to remove methods at any time. Exceptions: A method may not be deleted when it or any of the other methods for the same generic function are executing. This function has no return value.

13.10.7 Previewing a Generic Function Call

This debugging function lists all applicable methods for a particular generic function call in order of decreasing precedence (see section 8.5.2). The function list defmethods is different in that it lists all methods for a generic function.

Syntax

(preview generic <generic-function-name> <expression>*)

This function does not actually execute any of the methods, but any side effects of evaluating the generic function arguments and any query parameter restrictions (see section 8.4.3) in methods do occur. The output for the first example in section 8.5.2 would be as follows:


Example

CLIPS> (preview-generic + 4 5)

+ #7 (INTEGER <qry>) (INTEGER <qry>)

+ #8 (INTEGER <qry>) (NUMBER)

+ #3 (INTEGER) (INTEGER)

+ #4 (INTEGER) (NUMBER)

+ #6 (NUMBER) (INTEGER <qry>)

+ #2 (NUMBER) (INTEGER)

+ #SYS1 (NUMBER) (NUMBER) ($? NUMBER)

+ #5 (NUMBER) (NUMBER) ($? PRIMITIVE)

CLIPS>

13.11 CLIPS Object Oriented Language (COOL) Commands

The following commands manipulate elements of COOL.

13.11.1 Class Commands

The following commands manipulate defclasses.

13.11.1.1 Displaying the Text of a Defclass

Displays the text of a given defclass. This function has no return value.

Syntax

(ppdefclass <class-name>)

13.11.1.2 Displaying the List of Defclasses

Displays the names of all defclasses stored in the CLIPS environment. If <module name> is unspecified, then the names of all defclasses in the current module are displayed. If <module name> is specified, then the names of all defclasses in the specified module are displayed. If <module name> is the symbol *, then the names of all defclasses in all modules are displayed. This function has no return value.

Syntax

(list defclasses [<module-name>])

13.11.1.3 Deleting a Defclass

This function deletes a previously defined defclass and all its subclasses from the CLIPS environment.

Syntax

(undefclass <class-name>)


If the symbol * is used for <class name>, then all defclasses will be deleted (unless there exists a defclass called *). The undefclass command can be used to remove defclasses at any time. Exceptions: A defclass may not be deleted if it has any instances or if there is still a reference to it in another loaded construct, such as a generic function method. This function has no return value.

13.11.1.4 Examining a Class

This function provides a verbose description of a class including: abstract role (whether direct instances can be created or not), direct superclasses and subclasses, class precedence list, slots with all their facets and sources, and all recognized message handlers. This function has no return value.

Syntax

(describe class <class-name>)

Example

CLIPS>

(defclass CHILD (is-a USER)

(role abstract)

(multislot parents (cardinality 2 2))

(slot age (type INTEGER)

(range 0 18))

(slot sex (access read-only)

(type SYMBOL)

(allowed-symbols male female)

(storage shared)))

CLIPS>

(defclass BOY (is-a CHILD)

(slot sex (source composite)

(default male)))

CLIPS>

(defmessage-handler BOY play ()

(printout t “The boy is now playing…” crlf))

CLIPS> (describe-class CHILD)

====================================================================

********************************************************************

Abstract: direct instances of this class cannot be created.


Direct Superclasses: USER

Inheritance Precedence: CHILD USER OBJECT

Direct Subclasses: BOY

--------------------------------------------------------------------

SLOTS : FLD DEF PRP ACC STO MCH SRC VIS CRT OVRD-MSG SOURCE(S)

parents : MLT STC INH RW LCL RCT EXC PRV NIL put-parents CHILD

age : SGL STC INH RW LCL RCT EXC PRV NIL put-age CHILD

sex : SGL STC INH R SHR RCT EXC PRV NIL NIL CHILD


Constraint information for slots:


SLOTS : SYM STR INN INA EXA FTA INT FLT

parents : + + + + + + + + RNG:[-oo..+oo] CRD:[2..2]

age : + RNG:[0..18]

sex : #

-------------------------------------------------------------------

Recognized message-handlers:

init primary in class USER

delete primary in class USER

create primary in class USER

print primary in class USER

direct-modify primary in class USER

message-modify primary in class USER

direct-duplicate primary in class USER

message-duplicate primary in class USER

********************************************************************

====================================================================

CLIPS>


The following table explains the fields and their possible values in the slot descriptions:


| Field | Values | Explanation |

FLD SGL/MLT Field type (single field or multifield)
DEF STC/DYN/NIL Default value (static, dynamic or none)
PRP INH/NIL Propagation to subclasses (Inheritable or not inheritable)
ACC RW/R/INT Access (read write, read only or initialize only)
STO LCL/SHR Storage (local or shared)
MCH RCT/NIL Pattern match (reactive or non reactive)
SRC CMP/EXC Source type (composite or exclusive)
VIS PUB/PRV Visibility (public or private)
CRT R/W/RW/NIL Automatically created accessors (read, write, read-write or none)
OVRD-MSG <message-name> Name of message sent for slot overrides in make instance, etc.
SOURCE(S) <class-name>+ Source of slot (more than one class for composite)


In the constraint information summary for the slots, each of the columns shows one of the primitive data types . A + in the column means that any value of that type is allowed in the slot. A # in the column means that some values of that type are allowed in the slot. Range and cardinality constraints are displayed to the far right of each slot's row. The following table explains the abbreviations used in the constraint information summary for the slots:


| Abbreviation | Explanation |

SYM Symbol
STR String
INN Instance Name
INA Instance Address
EXA External Address
FTA Fact Address
INT Integer
FLT Float
RNG Range
CRD Cardinality

13.11.1.5 Examining the Class Hierarchy

This function provides a rudimentary display of the inheritance relationships between a class and all its subclasses. Indentation indicates a subclass. Because of multiple inheritance, some classes may appear more than once. Asterisks mark classes which are direct subclasses of more than one class. With no arguments, this function starts with the root class OBJECT. This function has no return value.

Syntax

(browse classes [<class-name>])

Example

CLIPS> (defclass a (is-a USER))

CLIPS> (defclass b (is-a USER))

CLIPS> (defclass c (is-a a b))

CLIPS> (defclass d (is-a USER))

CLIPS> (defclass e (is-a c d))

CLIPS> (defclass f (is-a e))

CLIPS> (browse-classes)

OBJECT

PRIMITIVE

NUMBER

INTEGER

FLOAT

LEXEME

SYMBOL

STRING

MULTIFIELD

ADDRESS

EXTERNAL-ADDRESS

FACT-ADDRESS

INSTANCE-ADDRESS *

INSTANCE

INSTANCE-ADDRESS *

INSTANCE-NAME

USER

INITIAL-OBJECT

a

c *

e *

f

b

c *

e *

f

d

e *

f

CLIPS>

13.11.2 Message handler Commands

The following commands manipulate defmessage handlers.

13.11.2.1 Displaying the Text of a Defmessage handler

Displays the text of a given defmessage handler. This function has no return value.

Syntax

Defaults are outlined.


(ppdefmessage handler <class-name> <handler-name>

[<handler-type>])

<handler-type> ::= around | before | primary | after

13.11.2.2 Displaying the List of Defmessage handlers

With no arguments, this function lists all handlers in the system. With one argument, this function lists all handlers for the specified class. If the optional argument “inherit” is given, inherited message handlers are also included. This function has no return value.

Syntax

(list defmessage handlers [<class-name> [inherit]])

Example

List all primary handlers in the system.


CLIPS> (defclass A (is-a USER))

CLIPS> (defmessage-handler A foo ())

CLIPS> (list-defmessage-handlers A)

foo primary in class A.

For a total of 1 message-handler.

CLIPS> (list-defmessage-handlers A inherit)

init primary in class USER.

delete primary in class USER.

create primary in class USER.

print primary in class USER.

foo primary in class A.

For a total of 4 message-handlers.

CLIPS>

13.11.2.3 Deleting a Defmessage handler

This function deletes a previously defined message handler.

Syntax

Defaults are outlined.


(undefmessage handler <class-name> <handler-name>

[<handler-type>])

<handler-type> ::= around | before | primary | after


An asterisk can be used to specify a wildcard for any of the arguments. (Wildcards will not work for the class name or handler name if there is a class or handler called *.) The undefmessage handler command can be used to remove handlers at any time. Exceptions: A handler may not be deleted when it or any of the other handlers for the same class are executing. This function has no return value.

Example

Delete all primary handlers in the system.


CLIPS> (undefmessage-handler * *)

CLIPS>

13.11.2.4 Previewing a Message

Displays a list of all the applicable message handlers for a message sent to an instance of a particular class. The level of indentation indicates the number of times a handler is shadowed, and lines connect the beginning and ending portions of the execution of a handler if it encloses shadowed handlers. The right double angle brackets indicate the beginning of handler execution, and the left double angle brackets indicate the end of handler execution. Message arguments are not necessary for a preview since they do not dictate handler applicability.

Syntax

(preview send <class-name> <message-name>)

Example

For the example in section 9.5.3, the output would be:


CLIPS> (preview-send USER my-message)

my-message around in class USER

| » my-message around in class OBJECT

| | » my-message before in class USER

| | « my-message before in class USER

| | » my-message before in class OBJECT

| | « my-message before in class OBJECT

| | » my-message primary in class USER

| | | » my-message primary in class OBJECT

| | | « my-message primary in class OBJECT

| | « my-message primary in class USER

| | » my-message after in class OBJECT

| | « my-message after in class OBJECT

| | » my-message after in class USER

| | « my-message after in class USER

| « my-message around in class OBJECT

« my-message around in class USER

CLIPS>

13.11.3 Definstances Commands

The following commands manipulate definstances.

13.11.3.1 Displaying the Text of a Definstances

Displays the text of a given definstances. This function has no return value.

Syntax

(ppdefinstances <definstances-name>)

13.11.3.2 Displaying the List of Definstances

Displays the names of all definstances stored in the CLIPS environment. This function has no return value.

Syntax

(list definstances)

13.11.3.3 Deleting a Definstances

This function deletes a previously defined definstances.

Syntax

(undefinstances <definstances-name>)


If the symbol * is used for <definstances name>, then all definstances will be deleted (unless there exists a definstances called *). The undefinstances command can be used to remove definstances at any time. Exceptions: A definstances may not be deleted when any of the instances in it are being created. This function has no return value.

13.11.4 Instances Commands

The following commands manipulate instances of user defined classes.

13.11.4.1 Listing the Instances

If no arguments are specified, all instances in scope of the current module are listed. If a module name is given, all instances within the scope of that module are given. If “*” is specified (and there is no module named “*”), all instances in all modules are listed (only instances which actually belong to classes of a module are listed for each module to prevent duplicates). If a class name is specified, only the instances for the named class are listed. If a class is specified, then the optional keyword inherit causes this function to list instances of subclasses of the class as well. This function has no return value.

Syntax

(instances [<module-name> [<class-name> [inherit]]])

13.11.4.2 Printing an Instance’s Slots from a Handler

This function operates implicitly on the active instance (see section 9.4.1.1) for a message, and thus can only be called from within the body of a message handler. This function directly prints the slots of the active instance and is the one used to implement the print handler attached to class USER (see section 9.4.4.3). This function has no return value.

Syntax

(ppinstance)

13.11.4.3 Saving Instances to a Text File

This function saves all instances in the CLIPS environment to the specified file in the following format:


(<instance-name> of <class-name> <slot-override>*)

<slot-override> ::= (<slot-name> <single-field-value>*)


A slot override is generated for every slot of every instance, regardless of whether the slot currently holds a default value or not. External address and fact address slot values are saved as strings. Instance address slot values are saved as instance names. This function returns the number of instances saved.

Syntax

(save instances <file-name>

[local | visible [[inherit] <class>+])


By default, save instances saves only the instances of all defclasses in the current module. Specifying visible saves instances for all classes within scope of the current module. Also, particular classes may be specified for saving, but they must be in scope according to the local or visible option. The inherit keyword can be used to force the saving of indirect instances of named classes as well (by default only direct instances are saved for named classes). Subclasses must still be in local or visible scope in order for their instances to be saved. Unless the inherit option is specified, only concrete classes can be specified. At least one class is required for the inherit option.


The file generated by this function can be loaded by either load instances or restore instances. save instances does not preserve module information, so the instance file should be loaded into the module which was current when it was saved.

13.11.4.4 Saving Instances to a Binary File

The function bsave instances works exactly like save instancesexcept that the instances are saved in a binary format which can only be loaded with the function bload instances. The advantage to this format is that loading binary instances can be much faster than loading text instances for large numbers of instances. The disadvantage is that the file is not usually portable to other platforms.

Syntax

(save instances <file-name>

[local | visible [[inherit] <class>+])

13.11.4.5 Loading Instances from a Text File

This function loads instances from a file into the CLIPS environment. It can read files created with save instances or any ASCII text file. Each instance should be in the format described in section 13.11.4.3 (although the instance name can be left unspecified). Calling load instances is exactly equivalent to a series of make instance calls (in CLIPS version 5.1, slot access restrictions, such as read only, were suspended during calls to load instances). This function returns the number of instances loaded or  1 if it could not access the instance file.

Syntax

(load instances <file-name>)

13.11.4.6 Loading Instances from a Text File without Message Passing

The function restore instances loads instances from a file into the CLIPS environment. It can read files created with save instances or any ASCII text file. Each instance should be in the format described in section 13.11.4.3 (although the instance name can be left unspecified). It is similar in operation to load instances, however, unlike load instances, restore instances does not use message passing for deletions, initialization, or slot overrides. Thus in order to preserve object encapsulation, it is recommended that restore instances only be used with files generated by save instances. This function returns the number of instances loaded or  1 if it could not access the instance file.

Syntax

(restore instances <file-name>)

13.11.4.7 Loading Instances from a Binary File

This function is similar to restore instances except that it can only work with files generated by bsave instances. See section 13.11.4.4 for a discussion of the merits of using binary instance files.

Syntax

(bload instances <file-name>)

13.12 Defmodule Commands

The following commands manipulate defmodule constructs.

13.12.1 Displaying the Text of a Defmodule

Displays the text of a given defmodule. This function has no return value.

Syntax

(ppdefmodule <defmodule-name>)

13.12.2 Displaying the List of Defmodules

Displays the names of all defmodule constructs stored in the CLIPS environment. This function has no return value.

Syntax

(list defmodules)

13.13 Memory Management Commands

The following commands display CLIPS memory status information. CLIPS memory management is described more fully in the Advanced Pro­gramming Guide.

13.13.1 Determining the Amount of Memory Used by CLIPS

Returns an integer representing the number of bytes CLIPS has currently in use or has held for later use. This number does not include operating system overhead for allocating memory.

Syntax

(mem used)

13.13.2 Determining the Number of Memory Requests Made by CLIPS

Returns an integer representing the number of times CLIPS has requested memory from the operating system. If the operating system overhead for allocating memory is known, then the total memory used can be calculated by


(+ (mem-used) (* <overhead-in-bytes> (mem-requests)))

Syntax

(mem requests)

13.13.3 Releasing Memory Used by CLIPS

Releases all free memory held internally by CLIPS back to the operating system. CLIPS will automatically call this function if it is running low on memory to allow the operating system to coalesce smaller memory blocks into larger ones. This function generally should not be called unless the user knows exactly what he/she is doing (since calling this function can prevent CLIPS from reusing memory efficiently and thus slow down performance). This function returns an integer representing the amount of memory freed to the operating system.

Syntax

(release mem)

13.13.4 Conserving Memory

Turns on or off the storage of information used for save and pretty print commands. This can save considerable memory in a large system. It should be called prior to loading any constructs. This function has no return value.

Syntax

(conserve mem <value>)


where value is either on or off.

13.14 On Line Help System

CLIPS provides an on line help facility for use from the top level interface. The help system uses CLIPS’ external text manipulation capabilities (see section 13.15). Thus, it is possible to add or change entries in the help file or to construct new help files with information specific to the user’s system.

13.14.1 Using the CLIPS Help Facility

The help facility displays menus of topics and prompts the user for a choice. It then references the help file for that information. The help facility can be called with or without a command line topic.

Syntax

(help [<path>])


where <path> is the full path leading to a topic in the help tree. For example, for information on defrule syntax, the user would type: (help construct_summary defrule). The help function has no return value.


Each element or field in the path is delimited by white space, and the help facility is not case sensitive. In addition, the entire name of a field does not need to be specified. Only enough characters to distinguish the field from other choices in the menu are neces­sary (if there is a conflict, the help facility will pick the first one in the list). For instance, (help con def) would be sufficient for the above example.


A few special fields can be used while in the help facility.


^ Branch up one level.

? When specified at the end of a path, this forces a display of the current menu, even on branch ups.

<nil> Giving no topic field will branch up one level.


A branch up from the MAIN topic root node implies an exit from help.


By default, the help facility comes up in the MAIN topic root menu and the user may make a choice as described above. The prompt line always displays the name of the current menu. The help facility will branch through the help tree until instructed to exit by a branch up from the top level. The level always is reset to the MAIN topic upon exit from the help facility.


The first call to the help facility will take longer than successive calls while the system loads help information into an internal lookup table. All other calls to the help facil­ity are very fast.

13.14.2 Finding the Help File

The help facility reads help information from a file during execution. Users may wish to change the location of the help file to meet the configuration of their system. The help path function was provided to allow this.

Syntax

(help path [<help-file-name>])


If no argument is specified, the function displays the name of the current help file. If an argument is specified, the help facility will use the new file name for future help refer­ences during this CLIPS session. To change the location of the help file permanently, a change must be made in the setup.h file, then CLIPS must be recompiled. The help path function has no return value.

13.15 External Text Manipulation

CLIPS provides a set of functions to build and access a hierarchical lookup system for multiple external files. Each file contains a set of text entries in a special format that CLIPS can later reference and display. The basic concept is that CLIPS retains a “map” of the text file in memory and can easily pull sections of text from the file without having to store the whole file in memory and without having to sequentially search the file for the appropriate text.

13.15.1 External Text File Format

Each external text file to be loaded into CLIPS must be described in a particular way. Each topic entry in each file must be in the format shown following.

Syntax

<level-num> <entry-type> BEGIN-ENTRY- <topic-name>

Topic information in form to be displayed when referenced.

END-ENTRY


The delimiter strings (lines with BEGIN_ENTRY or END_ENTRY info) must be the only things on their lines. Embedded white space between the fields of the delimiters is allowed.


The first parameter, <level num>, is the level of the hierarchical tree to which the entry belongs. The lower the number, the closer to the root level the topic is; i.e., the lowest level number indicates the root level. Subtopics are indicated by making the level number of the current topic larger than the previous entry (which is to be the parent). Thus, the tree must be entered in the file sequentially; i.e., a topic with all its subtopics must be described before going on to a topic at the same level. Entering a number less than that of the previous topic will cause the tree to be searched upwards until a level number is found which is less than the current one. The current topic then will be at­tached as a subtopic at that level. In this manner, multiple root trees may be created. Level number and order of entry in a file can indicate the order of precedence in which a list of subtopics that are all children of the same topic will be searched. Topics with the same level number will be searched in the order in which they appear in the file. Topics with lower level numbers will be searched first.

Example

0MBEGIN-ENTRY-ROOT
– Text –
END-ENTRY
2IBEGIN-ENTRY-SUBTOPIC1
– Text –
END-ENTRY
1IBEGIN-ENTRY-SUBTOPIC2
– Text –
END-ENTRY


In the above example, SUBTOPIC1 and SUBTOPIC2 are children of ROOT. However, in searching the children of ROOT, SUBTOPIC2 would be found first.


If the user wishes to access the information through the help facility (see section 13.14), the root node must be named MAIN. The contents of the MAIN menu may be changed.


The second parameter in the format defined above, the <entry type>, must be a single capital letter, either M (for MENU) or I (for INFORMATION). Only MENU entries may have subtopics.


The third parameter defined above, the <topic name>, can be any alphanumeric string of up to 80 characters. No white space can be embedded in the name.


Beginning a line with the delimiter “$$” forces the loader to treat the line as pure text, even if one of the key delimiters is in it. When the line is printed, the dollar signs are treated as blanks.

Example

0MBEGIN-ENTRY-ROOT1
– Root1 Text –
END-ENTRY
1MBEGIN-ENTRY-SUBTOPIC1
– Subtopic1 Text –
END-ENTRY
2IBEGIN-ENTRY-SUBTOPIC4
– Subtopic4 Text –
END-ENTRY
1IBEGIN-ENTRY-SUBTOPIC2
– Subtopic2 Text –
END-ENTRY
0IBEGIN-ENTRY-ROOT2
– Root2 Text –
END-ENTRY
-1MBEGIN-ENTRY-ROOT3
– Root3 Text –
END-ENTRY
0IBEGIN-ENTRY-SUBTOPIC3
– Subtopic3 Text –
END-ENTRY


Tree Diagram of Above Example :


 > ROOT3          > ROOT1          > ROOT2
| / \

| / \
V V V

SUBTOPIC3 SUBTOPIC1 SUBTOPIC2
|
|
V
SUBTOPIC4

13.15.2 External Text Manipulation Functions

The following functions are used by the help facility (see section 13.14) and can be used by users to maintain their own information system.

13.15.2.1 Fetch

The function fetch loads the named file (which must be in the format defined in section 13.15.1) into the internal lookup table.

Syntax

(fetch <file-name>)


The function returns the number of entries loaded if the fetch succeeded. If the file could not be loaded or was loaded already, the function returns the symbol FALSE.

The function print region looks up a specified entry in a particular file which has been loaded previously into the lookup table and prints the contents of that entry to the specified output.

Syntax

(print region <logical-name> <file-name> <topic-field>*)


where <logical name> is a name previously attached to an output device. To send the output to stdout, specify t for the logical name. <file name> is the name of the previously loaded file in which the entry is to be found, and the optional arguments, <topic field>*, is the full path of the topic entry to be found.


Each element or field in the path is delimited by white space, and the function is not case sensitive. In addition, the entire name of a field does not need to be specified. Only enough characters to distinguish the field from other choices at the same level of the tree are necessary. If there is a conflict, the function will pick the first one in the list. A few special fields can be specified.


^ Branch up one level.

? When specified at the end of a path, this forces a display of the current menu, even on branch ups.

<nil> Giving no topic field will branch up one level.


The level of the tree for a file remains constant between calls to print region. All levels count from menu only. Information levels do not count for branching up or down. To access an entry at the root level after branching down several levels in a previous call or series of calls, an equal number of branches up must be executed.

Examples

To display the entry for ROOT SUBTOPIC from the file foo.lis on the screen, type


(print-region t “foo.lis” ROOT SUBTOPIC)


or, using less characters,


(print-region t “foo.lis” roo sub)


Only one entry can be accessed per print region call. The function returns the symbol TRUE if the print region succeeded. If the entry was not found, it returns FALSE.


CLIPS> (fetch “foo.lis”)

7

CLIPS> (print-region t “foo.lis” roo sub)


– Subtopic3 Text –

TRUE

CLIPS> (print-region t “foo.lis” ”?“)


– Root3 Text –

TRUE

CLIPS> (print-region t “foo.lis” ^ root1 sub)


– Subtopic1 Text –

TRUE

CLIPS> (print-region t “foo.lis” sub)


– Subtopic4 Text –

TRUE

CLIPS> (print-region t “foo.lis” ^ subtopic2)


– Subtopic2 Text –

TRUE

CLIPS> (print-region t “foo.lis” ^ root2)


– Root2 Text –

TRUE

CLIPS> (toss “foo.lis”)

TRUE

CLIPS>

13.15.2.3 Toss

The function toss unloads the named file from the internal lookup table and releases the memory back to the system.

Syntax

(toss <file-name>)


The function returns the symbol TRUE if the toss succeeded. If the file was not on the lookup table, it returns FALSE.

13.16 Profiling Commands

The following commands provide the ability to profile CLIPS programs for performance.

13.16.1 Setting the Profiling Report Threshold

The set-profile-percent-threshold command sets the minimum percentage of time that must be spent executing a construct or user function for it to be displayed by the profile-info command. By default, the percent threshold is zero, so all constructs or user-functions that were profiled and executed at least once will be displayed by the profile-info command. The return value of this function is the old percent threshold.

Syntax

(set-profile-percent-threshold <number in the range 0 to 100>)

13.16.2 Getting the Profiling Report Threshold

The get-profile-percent-threshold command returns the current value of the profile percent threshold.

Syntax

(get-profile-percent-threshold)

13.16.3 Resetting Profiling Information

The profile-reset command resets all profiling information currently collected for constructs and user functions.

Syntax

(profile-reset)

13.16.4 Displaying Profiling Information

The profile-info command displays profiling information currently collected for constructs or user functions. Profiling information is displayed in six columns. The first column contains the name of the construct or user function profiled. The second column indicates the number of times the construct or user function was executed. The third column is the amount of time spent executing the construct or user function. The fourth column is the percentage of time spent in the construct or user function with respect to the total amount of time profiling was enabled. The fifth column is the total amount of time spent in the first execution of the construct or user function and all subsequent calls to other constructs/user functions. The sixth column is the percentage of this time with respect to the total amount of time profiling was enabled.

Syntax

(profile-info)

13.16.5 Profiling Constructs and User Functions

The profile command is used to enable/disable profiling of constructs and user functions. If constructs are profiled, then the amount of time spent executing deffunctions, generic functions, message handlers, and the RHS of defrules is tracked. If user-functions are profiled, then the time spent executing system and user defined functions is tracked. System defined functions include predefined functions available for your own use such as the < and numberp functions in addition to low level internal functions which are not available for your use (these will usually appear in profile-info output in all capital letters or surrounded by parentheses). It is not possible to profile constructs and user-functions at the same time. Enabling one disables the other. The off keyword argument disables profiling. Profiling can be repeatedly enable and disabled as long as only one of constructs or user-functions is consistently enabled. The total amount of time spent with profiling enabled will be displayed by the profile-info command. If profiling is enabled from the command prompt, it is a good idea to place the calls enabling and disabling profiling within a single progn function call. This will prevent the elapsed profiling time from including the amount of time needed to type the commands being profiled.

Syntax

(profile constructs | user-functions | off)

Example

CLIPS> (clear)

CLIPS> (deffacts start (fact 1))

CLIPS>

(deffunction function-1 (?x)

(bind ?y 1)

(loop-for-count (* ?x 10)

(bind ?y (+ ?y ?x))))

CLIPS>

(defrule rule-1

?f ← (fact ?x&:(< ?x 100))

(function-1 ?x)

(retract ?f)

(assert (fact (+ ?x 1))))

CLIPS>

(reset)

CLIPS>

(progn (profile constructs)

(run)

(profile off))

CLIPS> (profile-info)

Profile elapsed time = 0.474921 seconds


Construct Name Entries Time % Time+Kids %+Kids

-------------- ——- —— —– ——— ——


*** Deffunctions ***


function-1 99 0.436704 91.92% 0.436704 91.92%


*** Defrules ***


rule-1 99 0.027561 5.80% 0.464265 97.72%

CLIPS> (profile-reset)

CLIPS> (reset)

CLIPS>

(progn (profile user-functions)

(run)

(profile off))

CLIPS> (profile-info)

Profile elapsed time = 12.0454 seconds


Function Name Entries Time % Time+Kids %+Kids

------------- ——- —— —– ——— ——

retract 99 0.007953 0.07% 0.010646 0.09%

assert 99 0.012160 0.10% 0.032766 0.27%

run 1 0.047421 0.39% 12.045301 100.00%

profile 1 0.000049 0.00% 0.000049 0.00%

* 99 0.005579 0.05% 0.007610 0.06%

+ 49599 3.626217 30.10% 5.765490 47.86%

< 99 0.005234 0.04% 0.007749 0.06%

progn 49698 2.353003 19.53% 11.997880 99.61%

loop-for-count 99 1.481078 12.30% 11.910553 98.88%

PCALL 99 0.020747 0.17% 11.943234 99.15%

FACT_PN_VAR3 99 0.002515 0.02% 0.002515 0.02%

FACT_JN_VAR1 99 0.002693 0.02% 0.002693 0.02%

FACT_JN_VAR3 198 0.004718 0.04% 0.004718 0.04%

FACT_STORE_MULTIFIELD 99 0.005478 0.05% 0.012857 0.11%

PROC_PARAM 49599 1.036460 8.60% 1.036460 8.60%

PROC_GET_BIND 49500 1.102682 9.15% 1.102682 9.15%

PROC_BIND 49599 2.331363 19.35% 8.089474 67.16%

CLIPS> (set-profile-percent-threshold 1)

0.0

CLIPS> (profile-info)

Profile elapsed time = 12.0454 seconds


Function Name Entries Time % Time+Kids %+Kids

------------- ——- —— —– ——— ——

+ 49599 3.626217 30.10% 5.765490 47.86%

progn 49698 2.353003 19.53% 11.997880 99.61%

loop-for-count 99 1.481078 12.30% 11.910553 98.88%

PROC_PARAM 49599 1.036460 8.60% 1.036460 8.60%

PROC_GET_BIND 49500 1.102682 9.15% 1.102682 9.15%

PROC_BIND 49599 2.331363 19.35% 8.089474 67.16%

CLIPS> (profile-reset)

CLIPS> (profile-info)

CLIPS>


Appendix A   Support Information

A.1 Questions and Information

Inquiries related to the use or installation of CLIPS can be sent via electronic mail to clips@ghg.net.


The URL for the CLIPS World Wide Web page is http://www.ghg.net/clips/CLIPS.html. Usenet users can also find information and post questions about CLIPS to the comp.ai.shells news group. The CLIPS Frequently Asked Questions (FAQ) list can be found at the URL http://www.ghg.net/clips/CLIPS-FAQ.

A.2 CLIPS List Server

An electronic conferencing facility, sponsored by Distributed Computing Systems (http://www.discomsys.com), is also available to CLIPS users. Subscribers to this facility may send questions, observations, answers, editorials, etc., in the form of electronic mail to the conference. All subscribers will have a copy of these messages reflected back to them at their respective electronic mail addresses. To subscribe, send a single line message to clips request@discomsys.com containing the word “subscribe”. The subject field is ignored but the address found in the ‘Reply:’, ‘Reply to:’, or ‘From:’ field will be entered in the distribution list. Upon subscription you will receive a mail message instructing you how to participate in the conference from that point forward. Save this mail message. You may need the instructions later if you wish to unsubscribe from the list server.


To send your own messages to members of the conference you need simply address your mail to clips@discomsys.com. Your message will be reflected to all other members of the conference.

If you wish to remove yourself from the conference and discontinue receiving mail simply send a message to clips-request@discomsys.com with “unsubscribe” as the message text. If you want to unsubscribe using another email account than the one you subscribed with, then append the original subscribing email account to the text of the message. For example: “unsubscribe john.doe@account.net”. Do not send unsubscribe messages to clips@discomsys.com! This sends a mail message to every member of the list. If you need to get in contact with the list administrator (for trouble unsubscribing or other questions about the list), send email to clips-owner @discomsys.com.


Intelligent Software Professionals has made available the CLIPS-LIST archive, a WWW-based full text searchable archive containing over two years of question and answers directed to the CLIPS List Server. It can be accessed at the URL http://www.isphouston.com/swish-web.html.

A.3 CLIPS Developers’ Forum

The CLIPS Developers’ Forum, a thread-based message board, is available at http://www.cpbinc.com/clips. This board exists to provide a site for discussion of research, development, and implementation of the CLIPS expert systems and related technologies. The hosting services for this web page are provided by CPB, Inc.

A.4 Documentation

The CLIPS Reference Manuals and User's Guide are available in Portable Document Format (PDF) at the URL http://www.ghg.net/clips/download/documentation/. Adobe Acrobat Reader, which can be downloaded at http://www.adobe.com/prodindex/acrobat/readstep.html, is needed to view PDF files.


Expert Systems: Principles and Programming, 3rd Edition, by Giarratano and Riley (ISBN 0 534-95053-1 available for $75.95) comes with a CD-ROM containing CLIPS 6.05 executables (DOS, Windows 3.1/95, and MacOS), documentation, and source code. The first half of the book is theory oriented and the second half covers rule-based programming using CLIPS. For more information, contact:

International Thompson Publishing

7625 Empire Dr.

Florence, KY 41042

Phone: (800) 354-9706

Phone: (606) 525-2230


or


PWS Publishing Company

20 Park Plaza

Boston, MA 02116-4324

Phone: (617) 542-3377

Fax: (617) 338-6134

WWW: http://www.pws.com/pws.html

A.5 CLIPS Source Code and Executables

CLIPS executables can be downloaded from http://www.ghg.net/clips/download/executables/. The source code can be downloaded from http://www.ghg.net/clips/download/source/.


Appendix B   Update Release Notes

The following sections denote the changes and bug fixes for CLIPS versions 6.01, 6.02, 6.03, and 6.04, 6.05, 6.1, and 6.2.

B.1 Version 6.2

Environments – It is now possible in an embedded application to create multiple environments into which programs can be loaded. See section 9 of The Advanced Programming Guide for more details


New Microsoft Windows and MacOS X Interfaces – An improved Windows 95/98/NT CLIPS interface is now available for PC compatible computers. See section 2 of The Interfaces Guide for more details. An improved MacOS X/9.0 CLIPS interface is now available for Macintosh computers. See section 3 of The Interfaces Guide for more details.


COOL Default Behavior – For the purpose of role inheritance, system defined classes behave as concrete classes (see section 9.3.2.1). The default value for the create accessor facet is now read-write (see section 9.3.3.9). For the purpose of pattern-match inheritance, system defined classes behave as reactive classes unless the inheriting class is abstract (see section 9.3.2.2). This behavior can be restored to CLIPS 6.1 behavior using the set class defaults mode function (see section 12.16.1.25).


COOL Changes   The following changes have been made to instance behavior:


• Newly created instances are sent a create message (see sections 9.4.4.8 and 9.6.1).


New Functions and Commands   Several new functions and commands have been added. They are:


funcall (see section 12.7.10)


get-class-defaults-mode (see section 12.16.1.26)


set-class-defaults-mode (see section 12.16.1.25)


string-to-field (see section 12.3.12)


timer (see section 12.7.11)


Command and Function Enhancements   The following commands and functions have been enhanced:


switch (see section 12.6.9). The requirement of having at least two case statements has been removed.


printout (see section 12.4.2.3). The logical name nil now has special significance.


sort (see section 12.7.9). Multifield as well as single-field values can now be sorted.


random (see section 12.7.4). The integer value returned by the function can now be restricted to a specified range of values.


do-for-instance (see section 9.7.8.4). Multiple actions can be specified in the action portion of the query (which previously required an explicit progn call).


do-for-all-instances (see section 9.7.8.5). Multiple actions can be specified in the action portion of the query (which previously required an explicit progn call).


delayed-do-for-all-instances (see section 9.7.8.6). Multiple actions can be specified in the action portion of the query (which previously required an explicit progn call).


Bug Fixes   The following bugs were fixed by the 6.20 release:


• Inner member variables in nested instance set queries could be confused with member variables from an outer query. This would happen if the inner member variable name shared all of its characters with the first N characters of the outer variable name.


• Some data structures generated by object pattern matching were not garbage collected until a run command was issued.


• Backspaces were not properly handled in the display window of the Windows interface.


• The module name was not specified for deffunctions by the save command.


• Garbage collection triggered by evaluating the arguments to str-cat/sym-cat could change the value of the arguments already retrieved.


• The PutFactSlot C function does not properly increment/decrement the slot value that it changes.


• Defrule data structures could end up in an invalid state during a retract if a fact/object matched two patterns in a rule and one pattern was inside two nested not conditional elements and the other pattern was inside one not conditional element.


• The implode$ function does not properly handle the \ character in a string.


• Garbage collection triggered by expression evaluation during an assert-string call could corrupt the fact being asserted.


• Inappropriate fact syntax for the assert-string function causes a crash.


• The evaluation error flag was not reset before calling the AssertString C function.


• The FindDefclass C function crashes when the specified module is not defined.


• The save command did not always properly save constructs when modules using import/export specifications were used.

B.2 Version 6.1

C++ Compatible – The CLIPS source code can now be compiled using either an ANSI C or C++ compiler. Minimally, non-ANSI C compilers must support full ANSI style function prototypes and the void data type in order to compile CLIPS.


Profiling Commands – Several new commands provide the ability to profile the time spent in constructs and user-defined functions (see section 13.16).


Bug Fixes   The following bugs were fixed by the 6.10 release:


• Function modify-instance did not work properly under some circumstances.


• If the slot of an unrelated instance was changed during the initialization of another instance, the next reinitialization of the first instance would fail. Also, an initialize-only slot of an existing instance could be changed during the creation/initialization of another.


• Garbage collection could cause an internal CLIPS error when a multifield value returned by a function was generated by changing the start and/or end positions of an existing multifield.


• Calls to exit did not return a valid ANSI value for successful completion of the program.


• The temporary expression created by an eval function could inadvertently be garbage collected.


• Previous patch to CLIPS 6.05 to handle initialization of instances introduced new bug whereby initialize-only slots could not be set by init after handlers (or any time after the function init-slots was called).


• Memory could become corrupted when an error was encountered during a load-instances or restore-instances call.


• The Windows 95 CLIPS interface did not properly display strings containing two sequential carriage returns.


• Refresh and scroll bar bugs occurredwhen running the Windows 95 CLIPS interface under Windows NT.


New Functions and Commands   Several new functions and commands have been added. They are:


check-syntax (see section 12.3.11)

sort (see section 12.7.9)


Command and Function Enhancements   The following commands and functions have been enhanced:


format (see section 12.4.2.6). The c format flag allows a character to be displayed.

open (see section 12.4.2.1). Files can be opened with binary write access.

B.3 Version 6.05

Bug Fixes   The following bugs were fixed by the 6.05 release:


• Incremental reset did not work properly for some situations for rules containing or conditional elements.


• Version 6.0 binary save files were incompatible with version 6.04, but this situation was not detected.


• Garbage collection was not handled properly for facts in some situations.


• Explicitly deleting instances logically dependent on a partial match(es) on the LHS of rule could cause a crash when the truth maintenance system tried to implicitly delete those same instances when the logical support was removed.


• Direct slot access in a message-handler did not check to see if the active instance was stale potentially causing a crash.


• Comparison of atoms from object multifield slots across patterns would either always yield true or potentially cause a crash.


• The return value of the while and loop-for-count functions could inadvertently be garbage collected.


• Sharing of constant tests in object multifield slot patterns on the LHS of rules is not accomplished correctly in patterns where the constant test is the only test (not part of a compound expression) and is the last effective node in the pattern. This causes the affected patterns never to be matched.


• When a single-slot and a multislot from different classes could match the same pattern, memory was corrupted when the inference engine tried to retrieve variable bindings from an instance containing the single-slot.


• Functions insert$, slot-insert$, and direct-slot-insert$ could courrupt memory under certain circumstances.


• Incremental reset did not work properly under some circumstances for a newly added rule if the last shared join of the rule was connected to a not pattern CE.


• Active-instance-only functions, such as ppinstance, could be invalidly executed out of context by a deffunction, defrule, or defmethod called as a consequence of a message-handler action.


• Iteration loops for the delayed-do-for-all-instances function could prematurely garbage collect a value returned from the body of the loop.


• Function progn$ allowed unused ephemeral data to accumulate and not be garbage collected, thus causing a potential but unnecessary memory problem during the execution of the progn$ loop.


• Binary files were incorrectly saved when the environment contained more than 16,384 symbols, 16,384 integers, or 16,384 floating point

numbers.


• A crash could occur when objects matching patterns contained within a not conditional element were changed.


• The constant UNKNOWN in constant.h conflicted with an identical constant in an OS/2 header file.


• Subseq$ and mv-subseq functions did not always work properly.


• Initialization of instances could override slot changes made in put- message-handlers.


• The pretty print representation for multifield template slots didn’t work correctly in some situations.


• An implicit defgeneric foo could be created in one module when one was already imported from another module.


COOL Changes   The following changes have been made to instance behavior:


• A multifield value of length 1 is now a legal value for a single-field instance slot.


• Specifying no arguments in a slot-override or put causes the slot to be reset to its default value. This used to be illegal for single-field slots and caused multifield slots to be assigned a multifield value of zero length.


Command and Function Enhancements   The following commands and functions have been enhanced:


printout (see section 12.4.2.3). The symbols tab, vtab, and ff will print respectively a tab, a vertical tab, and a form feed.


member$ (see section 12.2.3). The first argument can be a multifield value.


exit (see section 13.1.7). The exit status code can now be specified.


load-instances and restore-instances (see sections 13.11.4.5 and 13.11.4.6). Instance names do not have to be specified in the instances file.


New Functions and Commands   Several new functions and commands have been added. They are:


delete-member$ (see section 12.2.14)

replace-member$ (see section 12.2.15)

slot-default-value (see section 12.16.1.24)

B.4 Version 6.04

New Functions and Commands   Several new functions and commands have been added. They are:


batch* (see section 13.1.10)

fact-existp (see section 12.9.7)

fact-relation (see section 12.9.8)

fact-slot-names (see section 12.9.10)

fact-slot-value (see section 12.9.9)

get-fact-list (see section 12.9.11)

load* (see section 13.1.2)


New Command Line Options   Two additional command line options, -f2 and -l, have been added (see section 2.1.2).


Bug Fixes   The following bugs were fixed by the 6.04 release:


• CLIPS would hang during an unwatch command if a binary file had been loaded that contained an or conditional element.


• An illformed construct name consisting of a module name and separater followed by a space would cause a crash.


• Embedding exclusively test CEs within not and/or and CEs did not work properly.


• Undefined variable errors in rules using an or CE could cause crashes.


• The GetNthWatchValue and GetNthWatchName functions in watch.c did not correctly update the pointer to the current watch item.


• Garbage collection during a load-instances call could prematurely remove symbols from the symbol table.


• Nested calls to CLIPSFunctionCall and other functions from an embedded application could cause premature garbage collection while a function is executing.

B.5 Version 6.03

Bug Fixes   The following bugs were fixed by the 6.03 release:


• The error message [INSMNGR11] was incorrectly labeled as [INSMNGR1111].


• Defglobals with initial values containing calls to assert or make-instance would have those values destroyed on a reset.


• Instance name restriction and type constraint conflicts were not detected.


• The function load-facts did not work for run-time modules.


• There were symbol garbage collection problems when using CLIPSFunctionCall from an embedded application.


• The default case of the switch function was handled incorrectly for binary save/load and constructs-to-c.


• Link errors were generated by the file factrhs.c when the DEFMODULE_CONSTRUCT compiler flag was set to zero.


• Conflicts between the type and allowed-values attributes were not detected.


• Dynamic constraint checking for multifield deftemplate slots did not work properly for some situations.

• Memory allocation problems existed on machines with architectures utilizing pointers and integers larger than 32-bits.

• When two object patterns containing more than one multifield reference shared at least one of those references, CLIPS could crash.

• The explicit getenv definition in edterm.c conflicted with the ANSI C stdlib.h definition.

• More than 32,768 references to a single symbol on machines with two byte integers would create internal errors.

• Errors generated when calling the Send C function from an embedded application would prevent subsequent calls from working correctly.

• Typing an ‘&’ in the Windows 3.1 CLIPS interface dialog window caused a ‘_’ to appear instead.

• Fact patterns in which a single slot contained more than one multifield variable didn’t always work properly.

• The isalpha library function did not return the correct value in the scanner.c module when ctype.h is included after stdio.h when creating a Win32 executable with Borland C++ v4.0.

• Errors in the argument string passed to CLIPSFunctionCall would cause subsequent calls to CLIPSFunctionCall to fail.

• Memory deallocation could work improperly if BLOCK_MEMORY was used and a memory block larger than the block memory table is deallocated.

• The set-strategy function returned the new value of the conflict resolution strategy rather than the old value.

• Redefining a deftemplate could cause a crash under some conditions.

• Selecting 32 character construct names in the construct browsers of the Windows 3.1 CLIPS interface would cause a crash.

• Constraint violations occurred for semantically correct rules containing multifield variables and expressions which referred to those variables.

• Messages could be sent to out of scope instances.

• The CLIPS System Error message was printed instead of an invalid slot name error message when invalid slot names were used.

B.6 Version 6.02

Bug Fixes   The following bugs were fixed by the 6.02 release:


• Some values which were legal to store in deftemplate slot were flagged by the constraint checker as being illegal.

• The code generated by the constructs-to-c command for rules with logical or or conditional elements would not compile.

• Loading a binary file with defglobals in it would cause a crash if defglobals were being watched.


• The use of the object-pattern-match-delay function could cause extraneous activations of rules.

• An inapplicable object pattern could be matched against an object if a great deal of object pattern-matching occurred over a long period of time.

• The function slot-types could corrupt memory when called for any slot that could hold an instance name.

• Instance-set query function iteration variables returned just base instance names. Thus, if one of the instances is from an imported class, other operations on that variable may not be able to access the instance.

• Read-only slots with a static default value were not automatically shared.

• The slot-cardinality function caused a crash when called for single-field slots.

• Link errors occured in insmngr.c when the DEFRULE_CONSTRUCT flag was disabled, but the LOGICAL_DEPENDENCIES flag was enabled in setup.h

• Calls to the return function within a progn$ function call did not work properly.

• Changing the focus on the RHS of a rule and then issuing a return command would remove the newly focused module and not the rule’s module from the focus stack.

• The cmptblty.h header file was not included in some of the distribution packages.


• Non-reactive instances which inherited reactive slots from a parent class could not be modified while pattern-matching was occurring.

• The instance-set query functions generated an invalid slot reference when the ‘:’ is the last character in a instance-set member variable name longer than two characters.

B.7 Version 6.01

Bug Fixes   The following bugs were fixed by the 6.01 release:


• The watch information for a rule was not correctly set when a rule was redefined.


• Calling the refresh-agenda command under certain circumstances would change the current setting of the salience evaluation attribute.


• The set-salience-evaluation function did not return the old value of the attribute.


• Under some situations, the wrong pattern CE number was printed when an error occurred in a rule.


• CLIPS would hang under certain conditions when attempting to print the rule in which an error occurred.


• Some internal CLIPS routines for accessing values from facts would cause crashes under some circumstances.


• The variable mixing error message (mixing single and multifield variables with the same name) was sometimes erroneously given.


• There were erroneous and missing error messages associated with constraint checking on the LHS of rules.


• Link errors were generated when the DEFMODULE_CONSTRUCT flag was disabled and CLIPS was being recompiled.


• Global variables were not exported properly by modules.


• One of the lines in the ClearReady function in the file constrct.c generated an error using some compilers.


• Instance names could not be entered at the command prompt.


Or CEs within not CEs were not always handled properly.


• A test CE used as the last CE in a not/and CE could cause variable comparisons that should not occur.


• Memory was not garbage collected when some embedded functions were used at the equivalent of the top-level command prompt.


• Using the return command to return a multifield value from within the while or loop for count functions did not work properly.

Appendix C   Glossary

This section defines some of the terminology used throughout this manual.


| abstraction | The definition of new classes to describe the common properties and behavior of a group of objects. |



action A function executed by a construct (such as the RHS of a rule) which typically has no return value, but performs some useful action (such as the printout action) (see section 12).


activation A rule is activated if all of its conditional elements are satisfied and it has not yet fired based on a specific set of matching pattern entities that caused it to be activated. Note that a rule can be activated by more than one set of pattern entities. An activated rule that is placed on the agenda is called an activation.


active instance The object responding to a message which can be referred to by ?self in the message’s handlers.


agenda A list of all rules that are presently ready to fire. It is sorted by salience values and the current conflict resolution strategy. The rule at the top of the agenda is the next rule that will fire.


antecedent The LHS of a rule.


bind The action of storing a value in a variable.


class Template for describing the common properties (slots) and behavior (message handlers) of a group of objects called instances of the class.


class precedence list A linear ordering of classes which describes the path of inheritance for a class.


command A function executed at the top level command prompt (such as the reset command) typically having no return value.


command prompt In the interactive interface, the “CLIPS>” prompt which indicates that CLIPS is ready for a command to be entered.


condition A conditional element.


conditional element A restriction on the LHS of a rule which must be satisfied in order for the rule to be applicable (also referred to as a CE).


| conflict resolution strategy | A method for determining the order in which rules should fire among rules with the same salience. There are seven different conflict resolution strategies: depth, breadth, simplicity, complexity, lex, mea, and random. |


| consequent | The RHS of a rule. |



constant A non varying single field value directly expressed as a series of characters.


constraint In patterns, a constraint is a requirement that is placed on the value of a field from a fact or instance that must be satisified in order for the pattern to be satisfied. For example, the ~red constraint is satisfied if the field to which the constraint is applied is not the symbol red. The term constraint is also used to refer to the legal values allowed in the slots of facts and instances.


construct A high level CLIPS abstraction used to add components to the knowledge base.


current focus The module from which activations are selected to be fired.


current module The module to which newly defined constructs that do not have a module specifier are added. Also is the default module for certain commands which accept as an optional argument a module name (such as list-defrules).


daemon A message handler which executes implicitly whenever some action is taken upon an object, such as initialization, deletion, or slot access.


deffunction A non overloaded function written directly in CLIPS.


deftemplate fact A deftemplate name followed by a list of named fields (slots) and specific values used to represent a deftemplate object. Note that a deftemplate fact has no inheritance. Also called a non ordered fact.


deftemplate object An informal term for the entity described by a deftemplate. A deftemplate object is simply an informal term for the collections of slots (without specific values) which define a deftemplate. Deftemplate objects do not have inheritance


deftemplate pattern A list of named constraints (constrained slots). A deftemplate pattern describes the attributes and associated values of a deftemplate object. Also called a non ordered pattern.


delimiter A character which indicates the end of a symbol. The following characters act as delimiters: any non printable ASCII character (including spaces, tabs, carriage returns, and line feeds), a double quote, opening and closing parenthesis “(” and “)”, an ampersand “&”, a vertical bar “|”, a less than “<”, a semicolon “;”, and a tilde “~”.


dynamic binding The deferral of which message handlers will be called for a message until run time.


encapsulation The requirement that all manipulation of instances of user defined classes be done with messages.


expression A function call with arguments specified.


external address The address of an external data structure returned by a function (written in a language such as C or Ada) that has been integrated with CLIPS (see section 2.3.1 for more details).


external function A function written in an external language (such as C or Ada) defined by the user or provided by CLIPS and called from within CLIPS rules.


facet A component of a slot specification for a class, e.g. default value and cardinality.


fact An ordered or deftemplate (non ordered) fact. Facts are the data about which rules rea­son and represent the current state of the world.


fact address A pointer to a fact obtained by binding a variable to the fact which matches a pattern on the LHS of a rule.


fact identifier A shorthand notation for referring to a fact. It consists of the character “f”, followed by a dash, followed by the fact index of the fact.


fact index A unique integer index used to identify a particular fact.


fact list The list of current facts.


field A placeholder (named or unnamed) that has a value.


fire A rule is said to have fired if all of its conditions are satisfied and the actions then are executed.


float A number that begins with an optional sign followed optionally in order by zero or more digits, a decimal point, zero or more digits, and an exponent (consisting of an e or E followed by an integer). A floating point number must have at least one digit in it (not including the exponent) and must either contain a decimal point or an exponent (see section 2.3.1 for more details).


focus As a verb, refers to changing the current focus. As a noun, refers to the current focus.


focus stack The list of modules that have been focused upon. The module at the top of the focus stack is the current focus. When all the activations from the current focus have been fired, the current focus is removed from the focus stack and the next module on the stack becomes the current focus.


function A piece of executable code identified by a specific name which returns a useful value or performs a useful side effect. Typically only used to refer to functions which do return a value (whereas commands and actions are used to refer to functions which do not return a value).


generic dispatch The process whereby applicable methods are selected and executed for a particular generic function call.


generic function A function written in CLIPS which can do different things depending on what the number and types of its arguments.


inference engine The mechanism provided by CLIPS which automatically matches patterns against the current state of the fact list and list of instances and determines which rules are applicable.


inheritance The process whereby one class can be defined in terms of other class(es).


instance An object is an instance of a class. Throughout the documentation, the term instance usually refers to objects which are instances of user defined classes.


instance (of a user defined class) An object which can only be manipulated via messages, i.e all objects except symbols, strings, integers, floats, multifields and external addresses.


instance address The address of an instance of a user defined class (see section 2.3.1 for more details).


instance name A symbol enclosed within left and right brackets (see section 2.3.1 for more details). An instance name refers to an object of the specified name which is an instance of a user defined class.


instance set An ordered collection of instances of user defined classes. Each member of an instance set is an instance of a set of classes, where the set can be different for each member.


instance set distributed action A user defined expression which is evaluated for every instance set which satisfies an instance set query.


instance set query A user defined boolean expression applied to an instance set to see if it satisfies further user defined criteria.


integer A number that begins with an optional sign followed by one or more digits (see section 2.3.1 for more details).


LHS Left Hand Side. The set of conditional elements that must be satisfied for the ac­tions of the RHS of a rule to be performed.


list A group of items with no implied order.


logical name A symbolic name that is associated with an I/O source or destination.


message The mechanism used to manipulate an object.


message dispatch The process whereby applicable message handlers are selected and executed for a particular message.


message handler An implementation of a message for a particular class of objects.


message handler precedence The property used by the message dispatch to select between handlers when more than one is applicable to a particular message.


method An implementation of a generic function for a particular set of argument restrictions.


method index A shorthand notation for referring to a method with a particular set of parameter restrictions.


method precedence The property used by the generic dispatch to select a method when more than one is applicable to a particular generic function call.


module A workspace where a set of constructs can be grouped together such that explicit control can be maintained over restricting the access of the constructs by other modules. Also used to control the flow of execution of rules through the use of the focus command.


module specifier A notation for specifying a module. It consists of a module name followed by two colons. When placed before a construct name, it’s used to specify which module a newly defined construct is to be added to or to specify which construct a command will affect if that construct is not in the current module.


multifield A sequence of unnamed placeholders each having a value.


multifield value A sequence of zero or more single field values.


non ordered fact A deftemplate fact.


number An integer or float.


object A symbol, a string, a floating point or integer number, a multifield value, an external address or an instance of a user defined class.


order Position is significant.


ordered fact A sequence of unnamed fields.


ordered pattern A sequence of constraints.


overload The process whereby a generic function can do different things depending on the types and number of its arguments, i.e. the generic function has multiple methods.


pattern A conditional element on the LHS of a rule which is used to match facts in the fact list.


pattern entity An item that is capable of matching a pattern on the LHS of a rule. Facts and instances are the only types of pattern entities available.


pattern matching The process of matching facts or instances to patterns on the LHS of rules.


polymorphism The ability of different objects to respond to the same message in a specialized manner.


primitive type object A symbol, string, integer, float, multifield or external address.


relation The first field in a fact or fact pattern. Synonomous with the associated deftemplate name.


RHS Right Hand Side. The actions to be performed when the LHS of a rule is satisfied.


rule A collection of conditions and actions. When all patterns are satisfied, the actions will be taken.


salience A priority number given to a rule. When multiple rules are ready for firing, they are fired in order of priority. The default salience is zero (0). Rules with the same salience are fired according to the current conflict resolution strategy.


sequence An ordered list.


shadowed message handler A message handler that must be explicitly called by another message handler in order to execute.


shadowed method A method that must be explicitly called by another method in order to execute.


single field value One of the primitive data types: float, integer, symbol, string, external address, instance name, or instance address.


slot Named single field or multifield. To write a slot give the field name (attribute) followed by the field value. A single field slot has one value, while a multifield slot has zero or more values. Note that a multifield slot with one value is strictly not the same as a single field slot. However, the value of a single field slot (or variable) may match a multifield slot (or multifield variable) that has one field.


slot accessor Implicit message handlers which provide read and write access to slots of an object.


specificity (class) A class that precedes another class in a class precedence list is said to be more specific. A class is more specific than any of its superclasses.


specificity (rule) A measure of how “specific” the LHS of a rule is in the pattern matching process. The specificity is determined by the number of constants, variables, and function calls used within LHS conditional elements.


string A set of characters that starts with double quotes (”) and is followed by zero or more printable characters and ends with double quotes (see section 2.3.1 for more details).


subclass If a class inherits from a second class, the first class is a subclass of the second class.


superclass If a class inherits from a second class, the second class is a superclass of the first class.


symbol Any sequence of characters that starts with any printable ASCII character and is followed by zero or more characters (see section 2.3.1 for more details).


top level In the interactive interface, the “CLIPS>” prompt which indicates that CLIPS is ready for a command to be entered.


value A single or multifield value.


variable An symbolic location which can store a value.

Appendix D   Integrated Editor

CLIPS includes a fully integrated version of the full screen MicroEMACS editor. You may call the editor from CLIPS, compile full buffers or just sections of the editor (incre­mental compile), temporarily exit the editor back to CLIPS, or permanently exit the editor. Since the editor is full screen, portions of it are highly machine dependent. As it is currently set up, the editor will run on VAX VMS machines using VT100  or VT240 compatible terminals, UNIX systems which support TERMCAP, the IBM PC, and most IBM compatibles.


The editor may be called from CLIPS with the following command:


(edit [“<file-name>”])


The file name is optional. If one is given, that file would be loaded. If no file name is given, the editor is entered without loading a file. Once in the file, all of the EMACS commands listed below are applicable. To exit the editor and clear all buffers, use <Ctrl Z> or <Ctrl X><Ctrl C>. To temporarily exit the editor and retain the information in the buffers, use <Ctrl X> Q. To compile a rules section, mark a region and type <Ctrl X><Ctrl T>. To compile the entire buffer, use <Meta T>. The editor can use exten­sive amounts of memory, and a flag is available in clips.h to remove all of the editor code.


When using the editor on multiuser machines like the VAX or many UNIX environ­ments, be careful with the control S and control Q commands; they could conflict with terminal XON/XOFF communications. All control S commands have a work around built into the editor. The save file command, normally <Ctrl X><Ctrl S>, is also <Meta> Z. The forward search command, normally <Ctrl S>, is also <Meta> J. The control Q command is rarely needed in a CLIPS file and, therefore, has no substi­tute.

D.1 Special characters

<del> Delete previous character (also <ctrl H> on some terminals).
<esc> Meta command prefix (also <ctrl [> on some terminals).

D.2 Control Commands

<ctrl @> Set mark at current position.
<ctrl A> Move cursor to beginning of line.
<ctrl B> Move cursor BACK one character.
<ctrl C> Start a new interactive command shell. Be careful!
<ctrl D> DELETE character under cursor.
<ctrl E> Move cursor to END of line.
<ctrl F> Move cursor FORWARD one character.
<ctrl G> Abort any command.
<ctrl H> (backspace) delete previous character.
<ctrl I> Insert a TAB.
<ctrl J> Insert a CR LF and indent next line.
<ctrl K> KILL (delete) to end of line.
<ctrl L> Redisplay screen.
<ctrl M> Insert a CR LF.
<ctrl N> Move cursor to NEXT line.
<ctrl O> OPEN a new line.
<ctrl P> Move to PREVIOUS line.
<ctrl Q> QUOTE the next character (insert the next character typed).
<ctrl R> Reverse SEARCH.
<ctrl S> Forward SEARCH (also <Meta J>).
<ctrl T> TRANSPOSE characters.
<ctrl U> Enter repeat count for next command.
<ctrl V> VIEW the next screen (scroll up one screen).
<ctrl W> KILL region (all text between cursor and last mark set).
<ctrl X> Extended command prefix   see below.
<ctrl Y> YANK (undelete) last text killed.
<ctrl Z> Quick save of file in current buffer (only) and exit.

D.3 Extended (Control X) Commands

<ctrl X>( Begin keyboard Macro.
<ctrl X>) End keyboard Macro.
<ctrl X>! Execute a single external command.
<ctrl X>= Show current cursor column and line number.
<ctrl X>: Go to a specific line number.
<ctrl X>1 Display current window only.
<ctrl X>2 Split the current window.
<ctrl X>B Switch to a different BUFFER.
<ctrl X>E EXECUTE keyboard Macro.
<ctrl X>F Set FILL column.
<ctrl X>K KILL a buffer (other than current buffer).
<ctrl X>M MATCH parenthesis (or {} or []).
<ctrl X>N Move to NEXT window.
<ctrl X>P Move to PREVIOUS window.
<ctrl X>R Global search and REPLACE (backwards).
<ctrl X>S Global SEARCH and replace (forwards).
<ctrl X>Z Enlarge current window by repeat count <ctrl U> lines.
<ctrl X><ctrl B> Show active BUFFERS.
<ctrl X><ctrl C> Exit without saving buffers.
<ctrl X><ctrl F> FIND file. Load if not already in buffer.
<ctrl X><ctrl N> Scroll current window up by repeat count lines.
<ctrl X><ctrl P> Scroll current window down by repeat count lines.
<ctrl X><ctrl R> RENAME file. Change file name for buffer.
<ctrl X><ctrl S> SAVE (write) current buffer into its file.
<ctrl X><ctrl V> VISIT a file. Read file and display in current window.
<ctrl X><ctrl W> WRITE buffer to file. Option to change name of file.
<ctrl X><ctrl Z> Reduce current window by repeat count lines.

D.4 Meta Commands (Activated by <esc> or <ctrl [>)

<meta>! Move current line to repeat count lines from top of window.
<meta» Move cursor to end of buffer.
<meta>< Move cursor to beginning of buffer.
<meta>. Set mark.
<meta>B Move cursor BACK one word.
<meta>C CAPITALIZE first letter of word.
<meta>D DELETE next word.
<meta>F Move cursor FORWARD one word.
<meta>J SEARCH forward (same as <ctrl S>).
<meta>L LOWERCASE (lowercase) next word.
<meta>R Query search and REPLACE (backwards).
<meta>S Query SEARCH and replace (forwards).
<meta>U UPPERCASE (uppercase) next word.
<meta>V VIEW the previous screen (scroll down one screen).
<meta>W COPY region into kill buffer.
<meta>Z SAVE current buffer into file (same as <ctrl X><ctrl S>).
<meta><del> DELETE previous word.

Appendix E   Performance Considerations

This appendix explains various techniques that the user can apply to a CLIPS program to maximize performance. Included are discussions of pattern ordering in rules, use of deffunctions in lieu of non overloaded generic functions, parameter restriction ordering in generic function methods, and various approaches to improving the speed of message passing and reading slots of instances.

E.1 Ordering of Patterns on the LHS

The issues which affect performance of a rule based system are considerably different from those which affect conventional programs. This section discusses the single most important issue: the ordering of patterns on the LHS of a rule.


CLIPS is a rule language based on the RETE algorithm. The RETE algorithm was de­signed specifically to provide very efficient pattern matching. CLIPS has attempted to implement this algorithm in a manner that combines efficient performance with powerful features. When used properly, CLIPS can provide very reasonable performance, even on microcomputers. However, to use CLIPS properly requires some under­stand­ing of how the pattern matcher works.


Prior to initiating execution, each rule is loaded into the system and a network of all patterns that appear on the LHS of any rule is constructed. As facts and instances of reactive classes (referred to collectively as pattern entities) are created, they are filtered through the pattern network. If the pattern entities match any of the patterns in the network, the rules associated with those patterns are partially instantiated. When pattern entities exist that match all patterns on the LHS of the rule, variable bindings (if any) are considered. They are considered from the top to the bottom; i.e., the first pattern on the LHS of a rule is con­sidered, then the second, and so on. If the variable bindings for all patterns are consis­tent with the constraints applied to the variables, the rules are activated and placed on the agenda.


This is a very simple description of what occurs in CLIPS, but it gives the basic idea. A number of important considerations come out of this. Basic pattern matching is done by filtering through the pattern network. The time involved in doing this is fairly constant. The slow portion of basic pattern matching comes from comparing variable bindings across patterns. Therefore, the single most important performance factor is the ordering of patterns on the LHS of the rule. Unfortunately, there are no hard and fast methods that will al­ways order the patterns properly. At best, there seem to be three “quasi” methods for ordering the patterns.


1) Most specific to most general. The more wildcards or unbound variables there are in a pattern, the lower it should go. If the rule firing can be controlled by a single pattern, place that pattern first. This technique often is used to provide control structure in an expert system; e.g., some kind of “phase” fact. Putting this kind of pattern first will guarantee that the rest of the rule will not be considered until that pattern exists. This is most effective if the single pattern consists only of literal constraints. If multiple patterns with variable bindings control rule firing, arrange the patterns so the most important variables are bound first and compared as soon as possible to the other pattern constraints. The use of phase facts is not recommended for large programs if they are used solely for controlling the flow of execution (use modules instead).


2) Patterns with the lowest number of occurrences in the fact list or instance list should go near the top. A large number of patterns of a particular form in the fact list or instance list can cause numerous partial instantiations of a rule that have to be “weeded” out by comparing the variable bindings, a slower operation.


3) Volatile patterns (ones that are retracted and asserted continuously) should go last, particularly if the rest of the patterns are mostly independent. Every time a pattern entity is created, it must be filtered through the network. If a pattern entity causes a partial rule instan­tiation, the variable bindings must be considered. By putting volatile patterns last, the variable bindings only will be checked if all of the rest of the patterns already exist.


These rules are not independent and commonly conflict with each other. At best, they provide some rough guidelines. Since all systems have these characteristics in different proportions, at a glance the most efficient manner of ordering patterns for a given system is not evident. The best approach is to develop the rules with minimal consideration of ordering. When the reasoning is fairly well verified, experiment with the patterns until the optimum configuration is found.


Another performance issue is the use of multifield variables and wildcards ($?). Although they provide a powerful capability, they must be used very carefully. Since they can bind to zero or more fields, they can cause multiple instantiations of a single rule. In particular, the use of multiple multifield variables in one pattern can cause a very large number of instantiations.


Some final notes on rule performance. Experience suggests that the user should keep the expert system “lean and mean.” The list of pattern entities should not be used as a data base for storage of ex­traneous information. Store and pattern match only on that information necessary for reasoning. Keep the pattern matching to a minimum and be as specific as possible. Many short, simple rules perform better than long, complex rules and have the added benefit of being easier to understand and maintain.

E.2 Deffunctions versus Generic Functions

Deffunctions execute more quickly than generic function because generic functions must first examine their arguments to determine which methods are applicable. If a generic function has only one method, a deffunction probably would be better. Care should be taken when determining if a particular function truly needs to be overloaded. In addition, if recompiling and relinking CLIPS is not prohibitive, user defined external functions are even more efficient than deffunctions. This is because deffunction are interpreted whereas external functions are directly executed. For more details, see sections 7 and 8.2.

E.3 Ordering of Method Parameter Restrictions

When the generic dispatch examines a generic function’s method to determine if it is applicable to a particular set of arguments, it examines that method’s parameter restrictions from left to right. The programmer can take advantage of this by placing parameter restrictions which are less frequently satisfied than others first in the list. Thus, the generic dispatch can conclude as quickly as possible when a method is not applicable to a generic function call. If a group of restrictions are all equally likely to be satisfied, placing the simpler restrictions first, such as those without queries, will also allow the generic dispatch to conclude more quickly for a method that is not applicable. For more details, see section 8.4.3.

E.4 Instance Addresses versus Instance Names

COOL allows instances of user defined classes to be referenced either by address or by name in functions which manipulate instances, such as message passing with the send function. However, when an instance is referenced by name, CLIPS must perform an internal lookup to find the instance address anyway. If the same instance is going to be manipulated many times, it might be advantageous to store the instance address and use that as a reference. This will allow CLIPS to always go directly to the instance. For more details, see sections 2.4.2 and 12.16.4.6.

E.5 Reading Instance Slots Directly

Normally, message passing must be used to read or set a slot of an instance. However, slots can be read directly within instance set queries and message handlers, and they can be set directly within message handlers. Accessing slots directly is significantly faster than message passing. Unless message passing is required (because of slot daemons), direct access should be used when allowed. For more details, see sections 9.4.2, 9.4.3, 9.4.4, 9.6.3, 9.6.4 and 9.7.3.


Appendix F   CLIPS Warning Messages

CLIPS typically will display two kinds of warning messages: those associated with executing constructs and those associated with loading constructs. This appendix describes some of the more common warning messages and what they mean. Each message begins with a unique identifier enclosed in brackets followed by the keyword WARNING; the messages are listed here in alphabetic order according to the identifier.


[CONSCOMP1] WARNING: Base file name exceeds 3 characters.

This may cause files to be overwritten if file name length

is limited on your platform.

The constructs to c command generates file names using the file name prefix supplied as an argument. If this base file name is longer than three characters, then the possibility exists that files may be overwritten if file name length is limited on your platform.


[CONSCOMP2] WARNING: Array name <arrayName> exceeds 6 characters in length. This variable may be indistinguishable from another by the linker.

The constructs to c command generates arrays for storing data structures. If the SHORT_LINK_NAMES compiler flag is enabled, then this warning message is displayed if generated array names exceed six characters in length.


[CSTRNBIN1] WARNING: Constraints are not saved with a binary image when dynamic constraint checking is disabled

or

[CSTRNCMP1] WARNING: Constraints are not saved with a constructs to c image when dynamic constraint checking is disabled

These warnings occur when dynamic constraint checking is disabled and the constructs to c or bsave commands are executed. Constraints attached to deftemplate and defclass slots will not be saved with the runtime or binary image in these cases since it is assumed that dynamic constraint checking is not required. Enable dynamic constraint checking with the set dynamic constraint checking function before calling constructs to c or bsave in order to include constraints in the runtime or binary image.


[DFFNXFUN1] WARNING: Deffunction <name> only partially deleted due to usage by other constructs.

During a clear or deletion of all deffunctions, only the actions of a deffunction were deleted because another construct which also could not be deleted referenced the deffunction.


Example:

CLIPS>

(deffunction foo ()

(printout t “Hi there!” crlf))

CLIPS>

(deffunction bar ()

(foo)

(undeffunction *))

CLIPS> (bar)


[GENRCBIN1] WARNING: COOL not installed! User defined class in method restriction substituted with OBJECT.

This warning occurs when a generic function method restricted by defclasses is loaded using the bload command into a CLIPS configuration where the object language is not enabled. The restriction containing the defclass will match any of the primitive types.


[OBJBIN1] WARNING: Around message handlers are notsupported in this environment.

This warning occurs when an around message handler is loaded using the bload command into a CLIPS configuration not supporting imperative message handlers.


[OBJBIN2] WARNING: Before and after message handlers are notsupported in this environment.

This warning occurs when a before or an after message handler is loaded using the bload command into a CLIPS configuration not supporting auxiliary message handlers.


Appendix G   CLIPS Error Messages

CLIPS typically will display two kinds of error messages: those associated with executing constructs and those associated with loading constructs. This appendix describes some of the more common error messages and what they mean. Each message begins with a unique identifier enclosed in brackets; the messages are listed here in alphabetic order according to the identifier.


[AGENDA1] Salience value must be an integer value.

Salience requires a integer argument and will otherwise result in this error message.


Example:

CLIPS> (defrule error (declare (salience a)) ⇒)


[AGENDA2] Salience value out of range <min> to <max>

The range of allowed salience has an explicit limit; this error message will result if the value is out of that range.


Example:

CLIPS> (defrule error (declare (salience 20000)) ⇒)


[AGENDA3] This error occurred while evaluating the salience [for rule <name>]

When an error results from evaluating a salience value for a rule, this error message is given.


[ANALYSIS1] Duplicate pattern address <variable name> found in CE <CE number>.

This message occurs when two facts or instances are bound to the same pattern address variable.


Example:

CLIPS> (defrule error ?f ← (a) ?f ← (b) ⇒)


[ANALYSIS2] Pattern address <variable name> used in CE #2 was previously bound within a pattern CE.

A variable first bound within a pattern cannot be later bound to a fact address.


Example:

CLIPS> (defrule error (a ?f) ?f ← (b) ⇒)


[ANALYSIS3] Variable <variable name> is used as both a single and multifield variable.

Variables on the LHS of a rule cannot be bound to both single and multifield variables.


Example:

CLIPS> (defrule error (a ?x $?x) ⇒)

[ANALYSIS4] Variable <variable name> [found in the expression <expression>]

was referenced in CE <CE number> <field or slot identifier> before being defined

A variable cannot be referenced before it is defined and, thus, results in this error message.


Example:

CLIPS> (defrule foo (a ~?x) ⇒)


[ARGACCES1] Function <name> expected at least <minimum> and no more than <maximum> argument(s)

This error occurs when a function receives less than the minimum number or more than the maximum number of argu­ment(s) expected.


[ARGACCES2] Function <function name> was unable to open file <file name>

This error occurs when the specified function cannot open a file.


[ARGACCES3] Function <name1> received a request from function <name2> for argument #<number> which is non existent

This error occurs when a function is passed fewer arguments than were expected.


[ARGACCES4] Function <name> expected exactly <number> argument(s)

This error occurs when a function that expects a precise number of argument(s) re­ceives an incorrect number of arguments.


[ARGACCES4] Function <name> expected at least <number> argument(s)

This error occurs when a function does not receive the minimum number of argu­ment(s) that it expected.


[ARGACCES4] Function <name> expected no more than <number> argument(s)

This error occurs when a function receives more than the maximum number of argu­ment(s) expected.


[ARGACCES5] Function <name> expected argument #<number> to be of type <data type>

This error occurs when a function is passed the wrong type of argument.


[ARGACCES6] Function <name1> received a request from function <name2> for argument #<number> which is not of type <data type>

This error occurs when a function requests from another function the wrong type of ar­gument, typically a string or symbol, when expecting a number or vice versa.


[BLOAD1] Cannot load <construct type> construct with binary load in effect.

If the bload command was used to load in a binary image, then the named construct cannot be entered until a clear command has been performed to remove the binary image.


[BLOAD2] File <file name> is not a binary construct file

This error occurs when the bload command is used to load a file that was not cre­ated with the bsave command.


[BLOAD3] File <file name> is an incompatible binary construct file

This error occurs when the bload command is used to load a file that was cre­ated with the bsave command using a different version of CLIPS.


[BLOAD4] The CLIPS environment could not be cleared.

Binary load cannot continue.

A binary load cannot be performed unless the current CLIPS environment can be cleared.


[BLOAD5] Some constructs are still in use by the current binary image:
<construct name 1>
<construct name 2>

<construct name N>

Binary <operation> cannot continue.

This error occurs when the current binary image cannot be cleared because some constructs are still being used. The <operation> in progress may either be a binary load or a binary clear.


[BLOAD6] The following undefined functions are referenced by this binary image:
<function name 1>
<function name 2>

<function name N>

This error occurs when a binary image is loaded that calls functions which were available in the CLIPS executable that originally created the binary image, but which are not available in the CLIPS executable that is loading the binary image.


[BSAVE1] Cannot perform a binary save while a binary load is in effect.

The bsave command does not work when a binary image is loaded.


[CLASSEXM1] Inherited slot <slot name> from class <slot name> is not valid for function slot publicp

This error message occurs when the function slot publicp is given an inherited slot. This function can only be used on slots defined in the given class.


Example:

CLIPS>

(defclass FOO (is-a USER)

(slot woz (visibility private)))

CLIPS>

(defclass BAR (is-a FOO))

CLIPS> (slot-publicp BAR woz)


[CLASSFUN1] Unable to find class <class name> in function <function name>.

This error message occurs when a function is given a non existent class name.


Example:

CLIPS> (class-slots FOO)


[CLASSFUN2] Maximum number of simultaneous class hierarchy traversals exceeded <number>.

This error is usually caused by too many simultaneously active instance set queries, e.g., do for all instances. The direct or indirect nesting of instance set query functions is limited in the following way:


Ci is the number of members in an instance set for the ith nested instance set query function.


N is the number of nested instance set query functions.


| |
⇐ 128 (the default upper limit) |


Example:

CLIPS>

(deffunction my-func ()

(do-for-instance ((?a USER) (?b USER) (?c USER)) TRUE

(printout t ?a “ ” ?b “ ” ?c crlf))

; The sum here is C1 = 3 which is OK.

CLIPS>

(do-for-all-instances ((?a OBJECT) (?b OBJECT)) TRUE

(my-func))


; The sum here is C1 + C2 = 2 + 3 = 5 which is OK.


The default upper limit of 128 should be sufficient for most if not all applications. However, the limit may be increased by editing the header file OBJECT.H and recompiling CLIPS.


[CLASSPSR1] An abstract class cannot be reactive.

Only concrete classes can be reactive.


Example:

CLIPS>

(defclass FOO (is-a USER)

(role abstract)

(pattern-match reactive))


[CLASSPSR2] Cannot redefine a predefined system class.

Predefined system classes cannot be modified by the user.


Example:

CLIPS> (defclass STRING (is-a NUMBER))


[CLASSPSR3] <name> class cannot be redefined while outstanding references to it still exist.

This error occurs when an attempt to redefine a class is made under one or both of the following two circumstances:


1) The class (or any of its subclasses) has instances.

2) The class (or any of its subclasses) appear in the parameter restrictions of any generic function method.


Before the class can be redefined, all such instances and methods must be deleted.


Example:

CLIPS> (defclass A (is-a USER))

CLIPS> (defmethod foo ((?a A LEXEME)))

CLIPS> (defclass A (is-a OBJECT)))


[CLASSPSR4] Class <attribute> already declared.

Only one specification of a class attribute is allowed.


Example:

CLIPS>

(defclass A (is-a USER)

(role abstract)

(role concrete))


[CLSLTPSR1] Duplicate slots not allowed.

Slots in a defclass must be unique.


Example:

CLIPS>

(defclass A (is-a USER)

(slot foo)

(slot foo))


[CLSLTPSR2] <name> facet already specified.

Only one occurrence of a facet per slot is allowed.


Example:

CLIPS>

(defclass A (is-a USER)

(slot foo (access read-only)

(access read-write)))


[CLSLTPSR3] Cardinality facet can only be used with multifield slots

Single field slots by definition have a cardinality of one.


Example:

CLIPS>

(defclass A (is-a USER)

(slot foo (cardinality 3 5)))


[CLSLTPSR4] read only slots must have a default value

Since slots cannot be unbound and read only slots cannot be set after initial creation of the instance, read only slots must have a default value.


Example:

CLIPS>

(defclass A (is-a USER)

(slot foo (access read-only)

(default ?NONE)))


[CLSLTPSR5] read only slots cannot have a write accessor

Since read only slots cannot be changed after initializationof the instance, a write accessor (put  message handler) is not allowed.


Example:

CLIPS>

(defclass A (is-a USER)

(slot foo (access read-only)

(create-accessor write)))


[CLSLTPSR6] no inherit slots cannot also be public

no inherit slots are by definition not accessible to subclasses and thus only visible to the parent class.


Example:

CLIPS>

(defclass A (is-a USER)

(slot foo (propagation no-inherit)

(visibility public)))


[COMMLINE1] Expected a '(', constant, or global variable

This message occurs when a top level command does not begin with a '(', constant, or global variable.


Example:

CLIPS> )

[COMMLINE2] Expected a command.

This message occurs when a top level command is not a symbol.


Example:

CLIPS> (“facts”


[CONSCOMP1] Invalid file name <fileName> contains '.'

A '.' cannot be used in the file name prefix that is passed to the constructs to c command since this prefix is used to generate file names and some operating systems do not allow more than one '.' to appear in a file name.


[CONSTRCT1] Some constructs are still in use. Clear cannot continue.

This error occurs when the clear command is issued when a construct is in use (such as a rule that is firing).


[CSTRCPSR1] Expected the beginning of a construct.

This error occurs when the load command expects a left parenthesis followed a construct type and these token types are not found.


[CSTRCPSR2] Missing name for <construct type> construct

This error occurs when the name is missing for a construct that requires a name.


Example:

CLIPS> (defgeneric ())


[CSTRCPSR3] Cannot define <construct type> <construct name> because of an import/export conflict.

or

[CSTRCPSR3] Cannot define defmodule <defmodule name> because of an import/export conflict cause by the <construct type> <construct name>.

A construct cannot be defined if defining the construct would allow two different definitions of the same construct type and name to both be visible to any module.


Example:

CLIPS> (defmodule MAIN (export ?ALL))

CLIPS> (deftemplate MAIN::foo)

CLIPS> (defmodule BAR (import MAIN ?ALL))

CLIPS> (deftemplate BAR::foo (slot x))


[CSTRCPSR4] Cannot redefine <construct type> <construct name> while it is in use.

A construct cannot be redefined while it is being used by another construct or other data structure (such as a fact or instance).


Example:

CLIPS> (clear)

CLIPS> (deftemplate bar)

CLIPS> (assert (bar))

<Fact-0>

CLIPS> (deftemplate (bar (slot x)))


[CSTRNCHK1] Message Varies

This error ID covers a range of messages indicating a type, value, range, or cardinality violation.


Example:

CLIPS> (deftemplate foo (slot x (type SYMBOL)))

CLIPS> (assert (foo (x 3)))


[CSTRNPSR1] The <first attribute name> attribute conflicts with the <second attribute name> attribute.

This error message occurs when two slot attributes conflict.


Example:

CLIPS> (deftemplate foo (slot x (type SYMBOL) (range 0 2)))


[CSTRNPSR2] Minimum <attribute> value must be less than

or equal to the maximum <attribute> value.

The minimum attribute value for the range and cardinality attributes must be less than or equal to the maximum attribute value for the attribute.


Example:

CLIPS> (deftemplate foo (slot x (range 8 1)))


[CSTRNPSR3] The <first attribute name> attribute cannot be used in conjunction with the <second attribute name> attribute.

The use of some slot attributes excludes the use of other slot attributes.


Example:

CLIPS> (deftemplate foo (slot x (allowed-values a)

(allowed-symbols b)))


[CSTRNPSR4] Value does not match the expected type for the <attribute name> attribute.

The arguments to an attribute must match the type expected for that attribute (e.g. integers must be used for the allowed integers attribute).


Example:

CLIPS> (deftemplate example (slot x (allowed-integers 3.0)))


[CSTRNPSR5] The cardinality attribute can only be used with multifield slots.

The cardinality attribute can only be used for slots defined with the multislot keyword.


Example:

CLIPS> (deftemplate foo (slot x (cardinality 1 1)))


[DEFAULT1] The default value for a single field slot must be a single field value

This error occurs when the default or default dynamic attribute for a single field slot does not contain a single value or an expression returning a single value.


Example:

CLIPS> (deftemplate error (slot x (default)))


[DFFNXPSR1] Deffunctions are not allowed to replace constructs.

A deffunction cannot have the same name as any construct.


Example:

CLIPS> (deffunction defgeneric ())


[DFFNXPSR2] Deffunctions are not allowed to replace external functions.

A deffunction cannot have the same name as any system or user defined external function.


Example:

CLIPS> (deffunction + ())


[DFFNXPSR3] Deffunctions are not allowed to replace generic functions.

A deffunction cannot have the same name as any generic function.


Example:

CLIPS> (defgeneric foo)

CLIPS> (deffunction foo ())


[DFFNXPSR4] Deffunction <name> may not be redefined while it is executing.

A deffunction can be loaded at any time except when a deffunction of the same name is already executing.


Example:

CLIPS>

(deffunction foo ()

(build “(deffunction foo ())”))

CLIPS> (foo)


[DFFNXPSR5] Defgeneric <name> imported from module <module name> conflicts with this deffunction.

A deffunction cannot have the same name as any generic function imported from another module.


Example:

CLIPS> (defmodule MAIN (export ?ALL))

CLIPS> (defmethod foo ())

CLIPS> (defmodule FOO (import MAIN ?ALL))

CLIPS> (deffunction foo)


[DRIVE1] This error occurred in the join network

Problem resides in join #<pattern number> in rule(s):

<problem rules>+

This error pinpoints other evaluation errors associated with evaluating an expression within the join network. The specific pattern of the problem rules is identified.


[EMATHFUN1] Domain error for <function name> function

This error occurs when an argument passed to a math function is not in the domain of values for which a return value exists.


[EMATHFUN2] Argument overflow for <function name> function

This error occurs when an argument to an extended math function would cause a numeric overflow.


[EMATHFUN3] Singularity at asymptote in <function name> function

This error occurs when an argument to a trigonometric math function would cause a singularity.


[EVALUATN1] Variable <name> is unbound

This error occurs when a local variable not set by a previous call to bind is accessed at the top level.


Example:

CLIPS> (progn ?error)


[EVALUATN2] No function, generic function or deffunction of name <name> exists for external call.

IThis error occurs only when an invalid function name is passed to the external C access routine CLIPSFunctionCall.


[EXPRNPSR1] A function name must be a symbol

In the following example, '~' is recognized by CLIPS as an operator, not a function:


Example:

CLIPS> (+ (~ 3 4) 4)


[EXPRNPSR2] Expected a constant, variable, or expression

In the following example, '~' is an operator and is illegal as an argument to a function call:


Example:

CLIPS> (⇐ ~ 4)


[EXPRNPSR3] Missing function declaration for <name>

CLIPS does not recognize <name> as a declared function and gives this error message.


Example:

CLIPS> (xyz)


[EXPRNPSR4] $ Sequence operator not a valid argument for <name>.

The sequence expansion operator cannot be used with certain functions.


Example:

CLIPS> (set-sequence-operator-recognition TRUE)

FALSE

CLIPS> (defrule foo (x $?y) ⇒ (assert (x1 $?y)))


[FACTMCH1] This error occurred in the pattern network

Currently active fact: <newly assert fact>

Problem resides in slot <slot name>

Of pattern #<pattern number> in rule(s):

<problem rules>+

This error pinpoints other evaluation errors associated with evaluating an expression within the pattern network. The specific pattern and field of the problem rules are identified.


[FACTMNGR1] Facts may not be retracted during pattern matching

or

[FACTMNGR2] Facts may not be retracted during pattern matching

Functions used on the LHS of a rule should not have side effects (such as the creation of a new instance or fact).


Example:

CLIPS>

(defrule error

(test (assert (blah)))

⇒)

CLIPS> (reset)


[FACTRHS1] Template <name> does not exist for assert.

This error occurs when an assert is attempted for a deftemplate which does not exist in a runtime or active bload image. In other situations, CLIPS will create an implied deftemplate if one does not already exist.


Example:

CLIPS> (clear)

CLIPS> (bsave error.bin)

TRUE

CLIPS> (bload error.bin)

TRUE

CLIPS> (assert (error))


[GENRCCOM1] No such generic function <name>in function undefmethod.

This error occurs when the generic function name passed to the undefmethod function does not exist.


Example:

CLIPS> (clear)

CLIPS> (undefmethod yak 3)


[GENRCCOM2] Expected a valid method index in function undefmethod.

This error occurs when an invalid method index is passed to undefmethod (e.g. a negative integer or a symbol other than *).


Example:

CLIPS> (defmethod foo ())

CLIPS> (undefmethod foo a))


[GENRCCOM3] Incomplete method specification for deletion.

It is illegal to specify a non wildcard method index when a wildcard is given for the generic function in the function undefmethod.


Example:

CLIPS> (undefmethod * 1)


[GENRCCOM4] Cannot remove implicit system function method for generic function <name>.

A method corresponding to a system defined function cannot be deleted.


Example:

CLIPS> (defmethod integer ((?x SYMBOL)) 0)

CLIPS> (list-defmethods integer)

integer #SYS1 (NUMBER)

integer #2 (SYMBOL)

For a total of 2 methods.

CLIPS> (undefmethod integer 1)


[GENRCEXE1] No applicable methods for <name>.

The generic function call arguments do not satisfy any method’s parameter restrictions.


Example:

CLIPS> (defmethod foo ())

CLIPS> (foo 1 2)


[GENRCEXE2] Shadowed methods not applicable in current context.

No shadowed method is available when the function call next method is called.


Example:

CLIPS> (call-next-method)


[GENRCEXE3] Unable to determine class of <value> in generic function <name>.

The class or type of a generic function argument could not be determined for comparison to a method type restriction.


Example:

CLIPS> (defmethod foo ((?a INTEGER)))

CLIPS> (foo [bogus-instance])


[GENRCEXE4] Generic function <name> method #<index> is not applicable to the given arguments.

This error occurs when call specific method is called with an inappropriate set of arguments for the specified method.


Example:

CLIPS> (defmethod foo ())

CLIPS> (call-specific-method foo 1 abc)


[GENRCFUN1] Defgeneric <name> cannot be modified while one of its methods is executing.

Defgenerics can’t be redefined while one of their methods is currently executing.


Example:

CLIPS> (defgeneric foo)

CLIPS> (defmethod foo () (build “(defgeneric foo)”))

CLIPS> (foo)

[GENRCFUN2] Unable to find method <name> #<index> in function <name>.

No generic function method of the specified index could be found by the named function.


Example:

CLIPS> (defmethod foo 1 ())

CLIPS> (ppdefmethod foo 2)


[GENRCFUN3] Unable to find generic function <name> in function <name>.

No generic function method of the specified index could be found by the named function.


Example:

CLIPS> (preview-generic balh)


[GENRCPSR1] Expected ')' to complete defgeneric.

A right parenthesis completes the definition of a generic function header.


Example:

CLIPS> (defgeneric foo ())


[GENRCPSR2] New method #<index1> would be indistinguishable from method #<index2>.

An explicit index has been specified for a new method that does not match that of an older method which has identical parameter restrictions.


Example:

CLIPS> (defmethod foo 1 ((?a INTEGER)))

CLIPS> (defmethod foo 2 ((?a INTEGER)))


[GENRCPSR3] Defgenerics are not allowed to replace constructs.

A generic function cannot have the same name as any construct.


[GENRCPSR4] Deffunction <name> imported from module <module name> conflicts with this defgeneric.

A deffunction cannot have the same name as any generic function imported from another module.


Example:

CLIPS> (defmodule MAIN (export ?ALL))

CLIPS> (deffunction foo ())

CLIPS> (defmodule FOO (import MAIN ?ALL))

CLIPS> (defmethod foo)


[GENRCPSR5] Generic functions are not allowed to replace deffunctions.

A generic function cannot have the same name as any deffunction.


[GENRCPSR6] Method index out of range.

A method index cannot be greater than the maximum value of an integer or less than 1.


Example:

CLIPS> (defmethod foo 0 ())

[GENRCPSR7] Expected a '(' to begin method parameter restrictions.

A left parenthesis must begin a parameter restriction list for a method.


Example:

CLIPS> (defmethod foo)


[GENRCPSR8] Expected a variable for parameter specification.

A method parameter with restrictions must be a variable.


Example:

CLIPS> (defmethod foo ((abc)))


[GENRCPSR9] Expected a variable or '(' for parameter specification.

A method parameter must be a variable with or without restrictions.


Example:

CLIPS> (defmethod foo (abc))


[GENRCPSR10] Query must be last in parameter restriction.

A query parameter restriction must follow a type parameter restriction (if any).


Example:

CLIPS> (defmethod foo ((?a (< ?a 1) INTEGER)))


[GENRCPSR11] Duplicate classes/types not allowed in parameter restriction.

A method type parameter restriction may have only a single occurrence of a particular class.


Example:

CLIPS> (defmethod foo ((?a INTEGER INTEGER)))


[GENRCPSR12] Binds are not allowed in query expressions.

Binding new variables in a method query parameter restriction is illegal.


Example:

CLIPS> (defmethod foo ((?a (bind ?b 1))))


[GENRCPSR13] Expected a valid class/type name or query.

Method parameter restrictions consist of zero or more class names and an optional query expression.


Example:

CLIPS> (defmethod foo ((?a 34)))


[GENRCPSR14] Unknown class/type in method.

Classes in method type parameter restrictions must already be defined.


Example:

CLIPS> (defmethod foo ((?a bogus-class)))


[GENRCPSR15] <name> class is redundant.

All classes in a method type parameter restriction should be unrelated.


Example:

CLIPS> (defmethod foo ((?a INTEGER NUMBER)))


[GENRCPSR16] The system function <name> cannot be overloaded.

Some system functions canot be overloaded.


Example:

CLIPS> (defmethod if ())


[GENRCPSR17] Cannot replace the implicit system method #<integer>.

A system function can not be overloaded with a method that has the exact number and types of arguments.


Example:

CLIPS> (defmethod integer ((?x NUMBER)) (* 2 ?x))


[GLOBLDEF1] Global variable <variable name> is unbound.

A global variable must be defined before it can be accessed at the command prompt or elsewhere.


Example:

CLIPS> (clear)

CLIPS> ?*x*


[GLOBLPSR1] Global variable <variable name> was referenced, but is not defined.

A global variable must be defined before it can be accessed at the command prompt or elsewhere.


Example:

CLIPS> (clear)

CLIPS> ?*x*


[INCRRSET1] The incremental reset behavior cannot be changed with rules loaded.

The incremental reset behaviour can only be changed when there are no currently defined rules.


[INHERPSR1] A class may not have itself as a superclass.

A class may not inherit from itself.


Example:

CLIPS> (defclass A (is-a A))


[INHERPSR2] A class may inherit from a superclass only once.

All direct superclasses of a class must be unique.


Example:

CLIPS> (defclass A (is-a USER USER))

[INHERPSR3] A class must be defined after all its superclasses.

Subclasses must be defined last.


Example:

CLIPS> (defclass B (is-a A))


[INHERPSR4] Must have at least one superclass.

All user defined classes must have at least one direct superclass.


Example:

CLIPS> (defclass A (is-a))


[INHERPSR5] Partial precedence list formed: <classa> <classb> … <classc>

Precedence loop in superclasses: <class1> <class2> … <classn> <class1>

No class precedence list satisfies the rules specified in section 9.3.1.1 for the given direct superclass list. The message shows a conflict for <class1> because the precedence implies that <class1> must both precede and succeed <class2> through <classn>. The full loop can be used to help identify which particular classes are causing the problem. This loop is not necessarily the only loop in the precedence list; it is the first one detected. The part of the precedence list which was successfully formed is also listed.


Example:

CLIPS> (defclass A (is-a MULTIFIELD FLOAT SYMBOL))

CLIPS> (defclass B (is-a SYMBOL FLOAT))

CLIPS> (defclass C (is-a A B))


[INHERPSR6] A user defined class cannot be a subclass of <name>.

The INSTANCE, INSTANCE NAME, and INSTANCE ADDRESS classes cannot have any subclasses.


Example:

CLIPS> (defclass A (is-a INSTANCE))


[INSCOM1] Undefined type in function <name>.

The evaluation of an expression yielded something other than a recognized class or primitive type.


[INSFILE1] Function <function name> could not completely process file <name>.

This error occurs when an instance definition is improperly formed in the input file for the load instances, restore instances, or bload instances command.


Example:

CLIPS> (load-instances bogus.txt)

[INSFILE2] <file name> file is not a binary instances file.

or

[INSFILE3] <file name> file is not a compatible binary instances file.

This error occurs when bload instances attempts to load a file that was not created with bsave instances or when the file being loaded was created by a different version of CLIPS.


Example:

CLIPS> (reset)

CLIPS> (save-instances foo.ins)

1

CLIPS> (bload-instances foo.ins)


[INSFILE4] Function bload instances unable to load instance <instance name>.

This error occurs when an instance specification in the input file for the bload instances command could not be created.


Example:

CLIPS> (defclass A (is-a USER) (role concrete))

CLIPS> (make-instance of A)

[gen1]

CLIPS> (bsave-instances foo.bin)

1

CLIPS> (clear)

CLIPS> (defclass A (is-a USER))

CLIPS> (bload-instances foo.bin)


[INSFUN1] Expected a valid instance in function <name>.

The named function expected an instance name or address as an argument.


Example:

CLIPS> (initialize-instance 34)


[INSFUN2] No such instance <name> in function <name>.

This error occurs when the named function cannot find the specified instance.


Example:

CLIPS> (instance-address [bogus-instance])

[INSFUN3] No such slot <name> in function <name>.

This error occurs when the named function cannot find the specified slot in an instance or class.


Example:

CLIPS> (defclass A (is-a USER))

CLIPS> (slot-writablep A b)


[INSFUN4] Invalid instance address in function <name>.

This error occurs when an attempt is made to use the address of a deleted instance.


Example:

CLIPS> (defclass A (is-a USER))

CLIPS> (make-instance a of A)

[a]

CLIPS> (defglobal ?*x* = (instance-address a))

CLIPS> (make-instance a of A)

[a]

CLIPS> (class ?*x*)


[INSFUN5] Cannot modify reactive instance slots while pattern matching is in process.

CLIPS does not allow reactive instance slots to be changed while pattern matching is taking place. Functions used on the LHS of a rule should not have side effects (such as the changing slot values).


Example:

CLIPS>

(defclass FOO (is-a USER)

(role concrete)

(pattern-match reactive)

(slot x (create-accessor read-write)))

CLIPS> (make-instance x of FOO)

[x]

CLIPS> (defrule BAR (x) (test (send [x] put-x 3)) ⇒)

CLIPS> (assert (x))


[INSFUN6] Unable to pattern match on shared slot <name> in class <name>.

This error occurs when the number of simultaneous class hierarchy traversals is exceeded while pattern matching on a shared slot. See the related error message [CLASSFUN2] for more details.


[INSFUN7] <multifield value> illegal for single field slot <name> of instance <name> found in <function call or message handler>.

Single field slots in an instance can hold only one atomic value.


Example:

CLIPS> (set-static-constraint-checking FALSE)

TRUE

CLIPS>

(defclass FOO (is-a USER)

(role concrete)

(slot foo))

CLIPS>

(defmessage-handler FOO error ()

(bind ?self:foo 1 2 3))

CLIPS> (make-instance foo of FOO)

[foo]

CLIPS> (send [foo] error)


[INSFUN8] Void function illegal value for slot <name> of instance <name> found in <function call or message handler>.

Only functions which have a return value can be used to generate values for an instance slot.


Example:

CLIPS> (set-static-constraint-checking FALSE)

TRUE

CLIPS>

(defclass FOO (is-a USER)

(role concrete)

(slot foo))

CLIPS>

(defmessage-handler FOO error ()

(bind ?self:foo (instances)))

CLIPS> (make-instance foo of FOO)

[foo]

CLIPS> (send [foo] error)


[INSMNGR1] Expected a valid name for new instance.

make instance expects a symbol or an instance name for the name of a new instance.


Example:

CLIPS> (make-instance 34 of A)


[INSMNGR2] Expected a valid class name for new instance.

make instance expects a symbol for the class of a new instance.


Example:

CLIPS> (make-instance a of 34)


[INSMNGR3] Cannot create instances of abstract class <name>.

Direct instances of abstract classes, such as the predefined system classes, are illegal.


Example:

CLIPS> (make-instance [foo] of USER)

[INSMGNR4] The instance <name> has a slot value which depends on the instance definition.

The initialization of an instance is recursive in that a slot override or default value tries to create or reinitialize the same instance.


Example:

CLIPS>

(defclass A (is-a USER)

(slot foo))

CLIPS>

(make-instance a of A (foo (make-instance a of A)))


[INSMNGR5] Unable to delete old instance <name>.

make instance will attempt to delete an old instance of the same name if it exists. This error occurs if that deletion fails.


Example:

CLIPS> (defclass A (is-a USER))

CLIPS>

(defmessage-handler A delete around ()

(if (neq (instance-name ?self) [a]) then

(call-next-handler)))

CLIPS> (make-instance a of A)

CLIPS> (make-instance a of A)


[INSMNGR6] Cannot delete instance <name> during initialization.

The evaluation of a slot override in make instance or initialize instance attempted to delete the instance.


Example:

CLIPS>

(defclass A (is-a USER)

(slot foo))

CLIPS>

(defmessage-handler A put-foo after ($?any)

(delete-instance))

CLIPS> (make-instance a of A (foo 2))


[INSMNGR7] Instance <name> is already being initialized.

An instance cannot be reinitialized during initialization.


Example:

CLIPS> (defclass A (is-a USER))

CLIPS> (make-instance a of A)

CLIPS>

(defmessage-handler A init after ()

(initialize-instance ?self))

CLIPS> (initialize-instance a)

CLIPS> (send [a] try)


[INSMNGR8] An error occurred during the initialization of instance <name>.

This message is displayed when an evaluation error occurs while the init message is executing for an instance.


[INSMNGR9] Expected a valid slot name for slot override.

make instance and initialize instance expect symbols for slot names.


Example:

CLIPS> (defclass A (is-a USER))

CLIPS> (make-instance a of A (34 override-value))


[INSMNGR10] Cannot create instances of reactive classes while pattern matching is in process.

CLIPS does not allow instances of reactive classes to be created while pattern matching is taking place. Functions used on the LHS of a rule should not have side effects (such as the creation of a new instance or fact).


Example:

CLIPS> (defclass FOO (is-a USER) (role concrete) (pattern-match reactive))

CLIPS> (defrule BAR (x) (test (make-instance of FOO)) ⇒)

CLIPS> (assert (x))


[INSMNGR11] Invalid module specifier in new instance name.

This error occurs when the module specifier in the instance name is illegal (such as an undefined module name).


Example:

CLIPS> (defclass FOO (is-a USER) (role concrete))

CLIPS> (make-instance BOGUS::x of FOO)


[INSMNGR12] Cannot delete instances of reactive classes while pattern matching is in process.

CLIPS does not allow instances of reactive classes to be deleted while pattern matching is taking place. Functions used on the LHS of a rule should not have side effects (such as the deletion of a new instance or the retraction of a fact).


Example:

CLIPS> (defclass FOO (is-a USER) (role concrete) (pattern-match reactive))

CLIPS> (make-instance x of FOO)

[x]

CLIPS> (defrule BAR (x) (test (send [x] delete)) ⇒)

CLIPS> (assert (x))


[INSMNGR13] Slot <slot name> does not exist in instance <instance name>.

This error occurs when the slot name of a slot override does not correspond to any of the valid slot names for an instance.


Example:

CLIPS> (defclass FOO (is-a USER) (role concrete))

CLIPS> (make-instance of FOO (x 3))


[INSMNGR14] Override required for slot <slot name> in instance <instance name>.

If the ?NONE keyword was specified with the default attribute for a slot, then a slot override must be provided when an instance containing that slot is created.


Example:

CLIPS> (defclass FOO (is-a USER)

(role concrete)

(slot x (default ?NONE)))

CLIPS> (make-instance of FOO)


[INSMNGR15] init slots not valid in this context.

The special function init slots (for initializing slots of an instance to the class default values) can only be called during the dispatch of an init message for an instance, i.e., in an init message handler.


Example:

CLIPS>

(defmessage-handler INITIAL-OBJECT error ()

(init-slots))

CLIPS> (reset)

CLIPS> (send [initial-object] error)


[INSMODDP1] Direct/message modify message valid only in modify instance.

The direct modify and message modify message handlers attached to the class USER can only be called as a result of the appropriate message being sent.by the modify instance or message modify instance functions. Additional handlers may be defined, but the message can only be sent in this context.


Example:

CLIPS> (reset)

CLIPS> (send [initial-object] direct-modify 0)


[INSMODDP2] Direct/message duplicate message valid only in duplicate instance.

The direct duplicate and message duplicate message handlers attached to the class USER can only be called as a result of the appropriate message being sent.by the duplicate instance or message duplicate instance functions. Additional handlers may be defined, but the message can only be sent in this context.


Example:

CLIPS> (reset)

CLIPS> (send [initial-object] direct-duplicate 0 0)


[INSMODDP3] Instance copy must have a different name in duplicate instance.

If an instance name is specified for the new instance in the call to duplicate instance, it must be different from the source instance’s name.


Example:

CLIPS> (reset)

CLIPS> (duplicate-instance initial-object to initial-object)

[INSMULT1] Function <name> cannot be used on single field slot <name> in instance <name>.

The functions described in section 12.13.4.12, such as slot insert$, can only operate on multifield slots.


Example:

CLIPS>

(defclass A (is-a USER)

(slot foo))

CLIPS> (make-instance a of A)

[a]

CLIPS> (slot-insert$ a foo 1 abc def)


[INSQYPSR1] Duplicate instance set member variable name in function <name>.

Instance set member variables in an instance set query function must be unique.


Example:

CLIPS> (any-instancep ((?a OBJECT) (?a OBJECT)) TRUE)


[INSQYPSR2] Binds are not allowed in instance set query in function <name>.

An instance set query cannot bind variables.


Example:

CLIPS>

(any-instancep ((?a OBJECT) (?b OBJECT))

(bind ?c 1))


[INSQYPSR3] Cannot rebind instance set member variable <name> in function <name>.

Instance set member variables cannot be changed within the actions of an instance set query function.


Example:

CLIPS>

(do-for-all-instances ((?a USER))

(if (slot-existp ?a age) then

(> ?a:age 30))

(bind ?a (send ?a get-brother)))


[IOFUN1] Illegal logical name used for <function name> function.

A logical name must be either a symbol, string, instance name, float, or integer.


Example:

(printout (create$ a b c) x)


[IOFUN2] Logical name <logical name> already in use.

A logical name cannot be associated with two different files.


Example:

CLIPS> (open “foo.txt” foo “w”)

TRUE

CLIPS> (open “foo2.txt” foo “w”)


[MEMORY1] Out of memory

This error indicates insufficient memory exists to expand internal struc­tures enough to allow continued operation (causing an exit to the operating system).


[MEMORY2] Release error in genfree

This error indicates a problem in the memory management routines.


[MEMORY3] Unable to allocate memory block > 32K

This error occurs when the bload function attempts to allocate a block of memory larger than 32K and the operating system does not permit blocks greater than 32K to be allocated. This will only occur on machines which have 2 byte integers (excluding the Macintosh and IBM PC which have machine dependent code provided so that they can allocate more than 32K). When this error occurs, CLIPS exits to the operating system.


[MISCFUN1] expand$ must be used in the argument list of a function call.

The expand$ function may not be called unless it is within the argument list of another function.


Example:

CLIPS> (expand$ (create$ a b c))


[MODULDEF1] Illegal use of the module specifier.

The module specifier can only be used as part of a defined construct’s name or as an argument to a function.


Example:

CLIPS> (deffunction y ())

CLIPS> (MAIN::y)


[MODULPSR1] Module <module name> does not export any constructs.

or

[MODULPSR1] Module <module name> does not export any <construct type> constructs.

or

[MODULPSR1] Module <module name> does not export the <construct type> <construct name>.

A construct cannot be imported from a module unless the defmodule exports that construct.


Example:

CLIPS> (clear)

CLIPS> (defmodule BAR)

CLIPS> (deftemplate BAR::bar)

CLIPS> (defmodule FOO (import BAR deftemplate bar)))


[MSGCOM1] Incomplete message handler specification for deletion.

It is illegal to specify a non wildcard handler index when a wildcard is given for the class in the external C function UndefmessageHandler(). This error can only be generated when a user defined external function linked with CLIPS calls this function incorrectly.


[MSGCOM2] Unable to find message handler <name> <type> for class <name> in function <name>.

This error occurs when the named function cannot find the specified message handler.


Example:

CLIPS> (ppdefmessage-handler USER foo around)


[MSGCOM3] Unable to delete message handlers.

This error occurs when a message handler can’t be deleted (such as when a binary image is loaded).


Example:

CLIPS> (defclass FOO (is-a USER) (role concrete))

CLIPS> (defmessage-handler FOO bar ())

CLIPS> (bsave foo.bin)

TRUE

CLIPS> (bload foo.bin)

TRUE

CLIPS> (undefmessage-handler FOO bar)


[MSGFUN1] No applicable primary message handlers found for <message>.

No primary message handler attached to the object’s classes matched the name of the message.


Example:

CLIPS> (defclass A (is-a USER))

CLIPS> (make-instance a of A)

[a]

CLIPS> (send [a] bogus-message)


[MSGFUN2] Message handler <name> <type> in class <name> expected exactly/at least <number> argument(s).

The number of message arguments was inappropriate for one of the applicable message handlers.


Example:

CLIPS> (defclass A (is-a USER))

CLIPS> (defmessage-handler USER foo (?a ?b))

CLIPS> (make-instance a of A)

[a]

CLIPS> (send [a] foo)


[MSGFUN3] <name> slot in instance <name>: write access denied.

This error occurs when an attempt is made to change the value of a read only slot.


Example:

CLIPS>

(defclass A (is-a USER)

(slot foo (default 100)

(read-only)))

CLIPS> (make-instance a of A)

[a]

CLIPS> (send [a] put-foo)


[MSGFUN4] <function> may only be called from within message handlers.

The named function operates on the active instance of a message and thus can only be called by message handlers.


Example:

CLIPS> (ppinstance)


[MSGFUN5] <function> operates only on instances.

The named function operates on the active instance of a message and can only handle instances of user defined classes (not primitive type objects).


Example:

CLIPS>

(defmessage-handler INTEGER print ()

(ppinstance))

CLIPS> (send 34 print)


[MSGFUN6] Private slot <slot name> of class <class name> cannot be accessed directly by handlers attached to class <class name>

A subclass which inherits private slots from a superclass may not access those slots using the ?self variable. This error can also occur when a superclass tries to access via dynamic put or dynamic get a private slot in a subclass.


Example:

CLIPS> (defclass FOO (is-a USER) (role concrete) (slot x))

CLIPS> (defclass BAR (is-a FOO))

CLIPS> (defmessage-handler BAR yak () ?self:x)


[MSGFUN7] Unrecognized message handler type in defmessage handler.

Allowed message handler types include primary, before, after, and around.


Example:

CLIPS> (defmessage-handler USER foo behind ())


[MSGFUN8] Unable to delete message handler(s) from class <name>.

This error occurs when an attempt is made to delete a message handler attached to a class for which any of the message handlers are executing.


Example:

CLIPS> (reset)

CLIPS>

(defmessage-handler INITIAL-OBJECT error ()

(undefmessage-handler INITIAL-OBJECT error primary))

CLIPS> (send [initial-object] error)


[MSGPASS1] Shadowed message handlers not applicable in current context.

No shadowed message handler is available when the functioncall next handler or override next handler is called.


Example:

CLIPS> (call-next-handler)


[MSGPASS2] No such instance <name> in function <name>.

This error occurs when the named function cannot find the specified instance.


Example:

CLIPS> (instance-address [bogus-instance])


[MSGPASS3] Static reference to slot <name> of class <name> does not apply to <instance name> of <class name>.

This error occurs when a static reference to a slot in a superclass by a message handler attached to that superclass is incorrectly applied to an instance of a subclass which redefines that slot. Static slot references always refer to the slot defined in the class to which the message handler is attached.


Example:

CLIPS>

(defclass A (is-a USER)

(slot foo))

CLIPS>

(defclass B (is-a A)

(role concrete)

(slot foo))

CLIPS>

(defmessage-handler A access-foo ()

?self:foo)

CLIPS> (make-instance b of B)

[b]

CLIPS> (send [b] access-foo)


[MSGPSR1] A class must be defined before its message handlers.

A message handler can only be attached to an existing class.


Example:

CLIPS> (defmessage-handler bogus-class foo ())


[MSGPSR2] Cannot (re)define message handlers during execution of other message handlers for the same class.

No message handlers for a class can be loaded while any current message handlers attached to the class are executing.


Example:

CLIPS> (defclass A (is-a USER))

CLIPS> (make-instance a of A)

[a]

CLIPS>

(defmessage-handler A build-new ()

(build “(defmessage-handler A new ())”))

CLIPS> (send [a] build-new)


[MSGPSR3] System message handlers may not be modified.

There are four primary message handlers attached to the class USER which cannot be modified: init, delete, create and print.


Example:

CLIPS> (defmessage-handler USER init ())


[MSGPSR4] Illegal slot reference in parameter list.

Direct slot references are allowed only within message handler bodies.


Example:

CLIPS> (defmessage-handler USER foo (?self:bar))


[MSGPSR5] Active instance parameter cannot be changed.

?self is a reserved parameter for the active instance.


Example:

CLIPS>

(defmessage-handler USER foo ()

(bind ?self 1))


[MSGPSR6] No such slot <name> in class <name> for ?self reference.

The symbol following the ?self: reference must be a valid slot for the class.


Example:

CLIPS> (defclass FOO (is-a USER) (role concrete) (slot x))

CLIPS> (defmessage-handler FOO bar () ?self:y)


[MSGPSR7] Illegal value for ?self reference.

The symbol following the ?self: reference must be a symbol.


Example:

CLIPS> (defclass FOO (is-a USER) (role concrete) (slot x))

CLIPS> (defmessage-handler FOO bar () ?self:7)


[MSGPSR8] Message handlers cannot be attached to the class <name>.

Message handlers cannot be attached to the INSTANCE, INSTANCE ADDRESS, or INSTANCE NAME classes.


Example:

CLIPS> (defmessage-handler INSTANCE foo ())


[MULTIFUN1] Multifield index <index> out of range 1..<end range> in function <name>

or

[MULTIFUN1] Multifield index range <start>…<end> out of range 1..<end range> in function <name>

This error occurs when a multifield manipulation function is passed a single index or range of indices that does not fall within the specified range of allowed indices.


Example:

CLIPS> (delete$ (create$ a b c) 4 4)


[MULTIFUN2] Cannot rebind field variable in function progn$.

The field variable (if specified) cannot be rebound within the body of the progn$ function.


Example:

CLIPS> (progn$ (?field (create$ a)) (bind ?field 3))


[OBJRTBLD1] No objects of existing classes can satisfy pattern.

No objects of existing classes could possibly satisfy the pattern. This error usually occurs when a restriction placed on the is a attribute is incompatible with slot restrictions before it in the pattern.


Example:

CLIPS> (defclass A (is-a INITIAL-OBJECT) (slot foo))

CLIPS> (defrule error (object (foo ?) (is-a ~A)) ⇒)


[OBJRTBLD2] No objects of existing classes can satisfy <attribute name> restriction in object pattern.

The restrictions on <attribute> are such that no objects of existing classes (which also satisfy preceding restrictions) could possibly satisfy the pattern.


Example:

CLIPS> (defrule error (object (bad-slot ?)) ⇒)

[OBJRTBLD3] No objects of existing classes can satisfy pattern #<pattern num>.

No objects of existing classes could possibly satisfy the pattern. This error occurs when the constraints for a slot as given in the defclass(es) are incompatible with the constraints imposed by the pattern.


Example:

CLIPS>

(defclass FOO (is-a INITIAL-OBJECT)

(slot bar (type INTEGER)))

CLIPS>

(defclass BAR (is-a INITIAL-OBJECT)

(slot bar (type SYMBOL))

(slot woz))

CLIPS>

(defrule error

(x abc)

(object (bar 100) (woz ?))

(y def)

⇒)


[OBJRTBLD4] Multiple restrictions on attribute <attribute name> not allowed.

Only one restriction per attribute is allowed per object pattern.


Example:

CLIPS> (defrule error (object (is-a ?) (is-a ?)) ⇒)


[OBJRTBLD5] Undefined class in object pattern.

Object patterns are applicable only to classes of objects which are already defined.


Example:

CLIPS> (defrule error (object (is-a BOGUS)) ⇒)


[OBJRTMCH1] This error occurred in the object pattern network

Currently active instance: <instance name>

Problem resides in slot <slot name> field #<field index>

Of pattern #<pattern number> in rule(s):

<problem rules>+

This error pinpoints other evaluation errors associated with evaluating an expression within the object pattern network. The specific pattern and field of the problem rules are identified.


[PATTERN1] The symbol <symbol name> has special meaning and may not be used as a <use name>.

Certain keywords have special meaning to CLIPS and may not be used in situations that would cause an ambiguity.


Example:

CLIPS> (deftemplate exists (slot x))


[PATTERN2] Single and multifield constraints cannot be mixed in a field constraint

Single and multifield variable constraints cannot be mixed in a field constraint (this restriction does not include variables passed to functions with the predicate or return value constraints).


Example:

CLIPS> (defrule foo (a ?x $?y ?x&~$?y) ⇒)


[PRCCODE1] Attempted to call a <construct> which does not exist.

In a CLIPS configuration without deffunctions and/or generic functions, an attempt was made to call a deffunction or generic function from a binary image generated by the bsave command.


[PRCCODE2] Functions without a return value are illegal as <construct> arguments.

An evaluation error occurred while examining the arguments for a deffunction, generic function or message.


Example:

CLIPS> (defmethod foo (?a))

CLIPS> (foo (instances))


[PRCCODE3] Undefined variable <name> referenced in <where>.

Local variables in the actions of a deffunction, method, message handler, or defrule must reference parameters, variables bound within the actions with the bind function, or variables bound on the LHS of a rule.


Example:

CLIPS> (defrule foo ⇒ (+ ?a 3))


[PRCCODE4] Execution halted during the actions of <construct> <name>.

This error occurs when the actions of a rule, deffunction, generic function method or message handler are prematurely aborted due to an error.


[PRCCODE5] Variable <name> unbound [in <construct> <name>].

This error occurs when local variables in the actions of a deffunction, method, message handler, or defrule becomes unbound during execution as a result of calling the bind function with no arguments.


Example:

CLIPS> (deffunction foo () (bind ?a) ?a)

CLIPS> (foo)


[PRCCODE6] This error occurred while evaluating arguments for the <construct> <name>.

An evaluation error occurred while examining the arguments for a deffunction, generic function method or message handler.


Example:

CLIPS> (deffunction foo (?a))

CLIPS> (foo (+ (eval “(gensym)”) 2))


[PRCCODE7] Duplicate parameter names not allowed.

Deffunction, method or message handler parameter names must be unique.


Example:

CLIPS> (defmethod foo ((?x INTEGER) (?x FLOAT)))


[PRCCODE8] No parameters allowed after wildcard parameter.

A wildcard parameter for a deffunction, method or message handler must be the last parameter.


Example:

CLIPS> (defmethod foo (($?x INTEGER) (?y SYMBOL)))


[PRCDRPSR1] Cannot rebind count variable in function loop for count.

The special variable ?count cannot be rebound within the body of the loop for count function.


Example:

CLIPS> (loop-for-count (?count 10) (bind ?count 3))


[PRCDRPSR2] The return function is not valid in this context.

or

[PRCDRPSR2] The break function is not valid in this context.

The return and break functions can only be used within certain contexts (e.g. the break function can only be used within a while loop and certain instance set query functions).


Example:

CLIPS> (return 3)


[PRCDRPSR3] Duplicate case found in switch function.

A case may be specified only once in a switch statement.


Example:

CLIPS> (switch a (case a then 8) (case a then 9))


[PRNTUTIL1] Unable to find <item> <item name>

This error occurs when CLIPS cannot find the named item (check for typos).


[PRNTUTIL2] Syntax Error: Check appropriate syntax for <item>

This error occurs when the appropriate syntax is not used.


Example:

CLIPS> (if (> 3 4))


[PRNTUTIL3]

*** CLIPS SYSTEM ERROR ***

ID = <error id>

CLIPS data structures are in an inconsistent or corrupted state.

This error may have occurred from errors in user defined code.

**************************

This error indicates an internal problem within CLIPS (which may have been caused by user defined functions or other user code). If the problem cannot be located within user defined code, then the <error id> should be reported.


[PRNTUTIL4] Unable to delete <item> <item name>

This error occurs when CLIPS cannot delete the named item (e.g. a construct might be in use). One example which will cause this error is an attempt to delete a deffunction or generic function which is used in another construct (such as the RHS of a defrule or a default dynamic facet of a defclass slot).


[PRNTUTIL5] The <item> has already been parsed.

This error occurs when CLIPS has already parsed an attribute or declaration.


[PRNTUTIL6] Local variables cannot be accessed by <function or construct>.

This error occurs when a local variable is used by a function or construct that cannot use global variables.


Example:

CLIPS> (deffacts info (fact ?x))


[PRNTUTIL7] Attempt to divide by zero in <function name> function.

This error occurs when a function attempts to divide by zero.


Example:

CLIPS> (/ 3 0)


[ROUTER1] Logical name <logical_name> was not recognized by any routers

This error results because “Hello” is not recognized as a valid router name.


Example:

CLIPS> (printout “Hello” crlf)


[RULECSTR1] Variable <variable name> in CE #<integer> slot <slot name>

has constraint conflicts which make the pattern unmatchable.

or

[RULECSTR1] Variable <variable name> in CE #<integer> field #<integer>

has constraint conflicts which make the pattern unmatchable.

or

[RULECSTR1] CE #<integer> slot <slot name>

has constraint conflicts which make the pattern unmatchable.

or

[RULECSTR1] CE #<integer> field #<integer>

has constraint conflicts which make the pattern unmatchable.

This error occurs when slot value constraints (such as allowed types) prevents any value from matching the slot constraint for a pattern.


Example:

CLIPS> (deftemplate foo (slot x (type SYMBOL)))

CLIPS> (deftemplate bar (slot x (type FLOAT)))

CLIPS> (defrule yak (foo (x ?x)) (bar (x ?x)) ⇒)


[RULECSTR2] Previous variable bindings of <variable name> caused the type restrictions

for argument #<integer> of the expression <expression>

found in CE#<integer> slot <slot name> to be violated.

This error occurs when previous variable bindings and constraints prevent a variable from containing a value which satisfies the type constraints for one of a function’s parameters.


Example:

CLIPS> (deftemplate foo (slot x (type SYMBOL)))

CLIPS> (defrule bar (foo (x ?x&:(> ?x 3))) ⇒)


[RULECSTR3] Previous variable bindings of <variable name> caused the type restrictions

for argument #<integer> of the expression <expression>

found in the rule's RHS to be violated.

This error occurs when previous variable bindings and constraints prevent a variable from containing a value which satisfies the type constraints for one of a function’s parameters.


Example:

CLIPS> (deftemplate foo (slot x (type SYMBOL)))

CLIPS> (defrule bar (foo (x ?x)) ⇒ (printout t (+ ?x 1) crlf))


[RULELHS1] The logical CE cannot be used with a not/exists/forall CE.

Logical CEs can be placed outside, but not inside, a not/exists/forall CE.


Example:

CLIPS> (defrule error (not (logical (x))) ⇒)


[RULELHS2] A pattern CE cannot be bound to a pattern address within a not CE

This is an illegal operation and results in an error message.


Example:

CLIPS> (defrule error (not ?f ← (fact)) ⇒)


[RULEPSR1] Logical CEs must be placed first in a rule

If logical CEs are used, then the first CE must be a logical CE.


Example:

CLIPS> (defrule error (a) (logical (b)) ⇒)


[RULEPSR2] Gaps may not exist between logical CEs

Logical CEs found within a rule must be contiguous.


Example:

CLIPS> (defrule error (logical (a)) (b) (logical ©) ⇒)

[STRNGFUN1] Function build does not work in run time modules.

or

[STRNGFUN1] Function eval does not work in run time modules.

The build and eval functions do not work in run time modules because the code required for parsing is not available.


[STRNGFUN2] Some variables could not be accessed by the eval function.

Local variables cannot be accessed by the eval function.


Example:

CLIPS> (eval “?x”)


[SYSDEP1] No file found for  f option

This message occurs if the  f option is used when executing CLIPS, but no arguments are provided.


Example:

clips -f


[TEXTPRO1] Unable to access help file.

This error occurs when the external text processing system cannot open the specified help file, e.g., the file cannot be found or the CLIPS process does not have sufficient privileges to read the file.


Example:

CLIPS> (help-path “bogus.txt”)

CLIPS. (help)


[TEXTPRO2] Unable to load file. <Explanatory text>.

This error occurs when the external text processing system command fetch encounters an error when loading a file.


Example:

CLIPS> (fetch “bogus.txt”)


[TMPLTDEF1] Invalid slot <slot name> not defined in corresponding deftemplate <deftemplate name>

The slot name supplied does not correspond to a slot name defined in the corre­sponding deftemplate


Example:

CLIPS> (deftemplate example (slot x))

CLIPS> (defrule error (example (z 3)) ⇒)


[TMPLTDEF2] The single field slot <slot name> can only contain a single field value.

If a slot definition is specified in a template pattern or fact, the contents of the slot must be capable of matching against or evaluating to a single value.


Example:

CLIPS> (deftemplate example (slot x))

CLIPS> (assert (example (x)))


[TMPLTFUN1] Fact indexes can only be used by <command name> as a top level command.

Fact indexes may only be used with the modify and duplicate commands when the command is issued from the top level command prompt.


Example:

CLIPS> (defrule foo ⇒ (modify 1 (x 3))


[TMPLTFUN2] Attempted to assert a multifield value into the single field slot <slot name> of deftemplate <deftemplate name>.

A multifield value cannot be stored in a single field slot.


Example:

CLIPS> (deftemplate foo (slot x))

CLIPS>

(defrule foo

(bind ?x (create$ a b))

(assert (foo (x ?x))))

CLIPS> (reset)

CLIPS> (run)


[TMPLTRHS1] Slot <slot name> requires a value because of its (default ?NONE) attribute.

The (default ?NONE) attribute requires that a slot value be supplied whenever a new fact is created.


Example:

CLIPS> (deftemplate foo (slot x (default ?NONE)))

CLIPS> (assert (foo))

Appendix H   CLIPS BNF

Data Types


<symbol> ::= A valid symbol as specified

in section 2.3.1


<string> ::= A valid string as specified

in section 2.3.1


<float> ::= A valid float as specified

in section 2.3.1


<integer> ::= A valid integer as specified

in section 2.3.1


<instance-name> ::= A valid instance name as specified

in section 2.3.1


<number> ::= <float> | <integer>


<lexeme> ::= <symbol> | <string>


<constant> ::= <symbol> | <string> | <integer> |

<float> | <instance name>


<comment> ::= <string>


<variable-symbol> ::= A symbol beginning with an

alphabetic character


<function-name> ::= Any symbol which corresponds to a

system or user defined function, a

deffunction name, or a defgeneric

name


<file-name> ::= A symbol or string which is a valid

file name (including path

information) for the operating

system under which CLIPS is running


<slot-name> ::= A valid deftemplate slot name


<…-name> ::= A <symbol> where the ellipsis

indicate what the symbol represents.

For example, <rule-name> is a symbol

which represents the name of a rule.

Variables and Expressions


<single-field-variable> ::= ?<variable-symbol>


<multifield-variable> ::= $?<variable-symbol>


<global-variable> ::= ?*<symbol>*


<variable> ::= <single-field-variable> |

<multifield-variable> |

<global-variable>


<function-call> ::= (<function-name> <expression>*)


<expression> ::= <constant> | <variable> |

<function-call>


<action> ::= <expression>


<…-expression> ::= An <expression> which returns

the type indicated by the

ellipsis. For example,

<integer-expression> should

return an integer.

Constructs


<CLIPS-program> ::= <construct>*


<construct> ::= <deffacts-construct> |

<deftemplate-construct> |

<defglobal-construct> |

<defrule-construct> |

<deffunction-construct> |

<defgeneric-construct> |

<defmethod-construct> |

<defclass-construct> |

<definstance-construct> |

<defmessage-handler-construct> |

<defmodule-construct>

Deffacts Construct


<deffacts-construct> ::= (deffacts <deffacts-name> [<comment>]
<RHS-pattern>*)

Deftemplate Construct


<deftemplate-construct>

::= (deftemplate <deftemplate-name>

[<comment>]

<slot-definition>*)


<slot-definition> ::= <single-slot-definition> |

<multislot-definition>


<single-slot-definition>

::= (slot <slot-name> <template-attribute>*)


<multislot-definition>

::= (multislot <slot-name>

<template-attribute>*)


<template-attribute>

::= <default-attribute> |

<constraint-attribute>


<default-attribute>

::= (default ?DERIVE | ?NONE | <expression>*) |

(default-dynamic <expression>*)

Fact Specification


<RHS-pattern> ::= <ordered-RHS-pattern> |

<template-RHS-pattern>


<ordered-RHS-pattern> ::= (<symbol> <RHS-field>+)


<template-RHS-pattern> ::= (<deftemplate-name> <RHS-slot>*)


<RHS-slot> ::= <single-field-RHS-slot> |

<multifield-RHS-slot>


<single-field-RHS-slot> ::= (<slot-name> <RHS-field>)


<multifield-RHS-slot> ::= (<slot-name> <RHS-field>*)


<RHS-field> ::= <variable> |

<constant> |

<function-call>

Defrule Construct


<defrule-construct> ::= (defrule <rule-name> [<comment>]

[<declaration>]

<conditional-element>*

<action>*)

<declaration> ::= (declare <rule-property>+)


<rule-property> ::= (salience <integer-expression>) |

(auto-focus <boolean-symbol>)

<boolean-symbol> ::= TRUE | FALSE


<conditional-element> ::= <pattern-CE> |

<assigned-pattern-CE> |

<not-CE> | <and-CE> | <or-CE> |

<logical-CE> | <test-CE> |

<exists-CE> | <forall-CE>


<pattern-CE> ::= <ordered-pattern-CE> |

<template-pattern-CE> |

<object-pattern-CE>


<assigned-pattern-CE> ::= <single-field-variable> ← <pattern-CE>


<not-CE> ::= (not <conditional-element>)


<and-CE> ::= (and <conditional-element>+)

<or-CE> ::= (or <conditional-element>+)


<logical-CE> ::= (logical <conditional-element>+)


<test-CE> ::= (test <function-call>)


<exists-CE> ::= (exists <conditional-element>+)


<forall-CE> ::= (forall <conditional-element>

<conditional-element>+)


<ordered-pattern-CE> ::= (<symbol> <constraint>*)


<template-pattern-CE> ::= (<deftemplate-name> <LHS-slot>*)


<object-pattern-CE> ::= (object <attribute-constraint>*)


<attribute-constraint> ::= (is-a <constraint>) |

(name <constraint>) |

(<slot-name> <constraint>*)


<LHS-slot> ::= <single-field-LHS-slot> |

<multifield-LHS-slot>


<single-field-LHS-slot> ::= (<slot-name> <constraint>)


<multifield-LHS-slot> ::= (<slot-name> <constraint>*)


<constraint> ::= ? | $? | <connected-constraint>


<connected-constraint>

::= <single-constraint> |

<single-constraint> & <connected-constraint> |

<single-constraint> | <connected-constraint>


<single-constraint> ::= <term> | ~<term>


<term> ::= <constant> |

<single-field-variable> |

<multifield-variable> |

:<function-call> |

=<function-call>

Defglobal Construct

<defglobal-construct> ::= (defglobal [<defmodule-name>]

<global-assignment>*)


<global-assignment> ::= <global-variable> = <expression>


<global-variable> ::= ?*<symbol>*

Deffunction Construct


<deffunction-construct>

::= (deffunction <name> [<comment>]

(<regular-parameter>* [<wildcard-parameter>])

<action>*)


<regular-parameter> ::= <single-field-variable>


<wildcard-parameter> ::= <multifield-variable>

Defgeneric Construct


<defgeneric-construct> ::= (defgeneric <name> [<comment>])

Defmethod Construct


<defmethod-construct>

::= (defmethod <name> [<index>] [<comment>]

(<parameter-restriction>*

[<wildcard-parameter-restriction>])

<action>*)


<parameter-restriction>

::= <single-field-variable> |

(<single-field-variable> <type>* [<query>])


<wildcard-parameter-restriction>

::= <multifield-variable> |

(<multifield-variable> <type>* [<query>])


<type> ::= <class-name>


<query> ::= <global-variable> | <function-call>

Defclass Construct


<defclass-construct> ::= (defclass <name> [<comment>]

(is-a <superclass-name>+)

[<role>]

[<pattern-match-role>]

<slot>*

<handler-documentation>*)


<role> ::= (role concrete | abstract)


<pattern-match-role>

::= (pattern-match reactive | non-reactive)


<slot> ::= (slot <name> <facet>*) |

(single-slot <name> <facet>*) |

(multislot <name> <facet>*)


<facet> ::= <default-facet> | <storage-facet> |

<access-facet> | <propagation-facet> |

<source-facet> | <pattern-match-facet> |

<visibility-facet> | <create-accessor-facet>

<override-message-facet> | <constraint-attribute>

<default-facet> ::=

(default ?DERIVE | ?NONE | <expression>*) |

(default-dynamic <expression>*)


<storage-facet> ::= (storage local | shared)


<access-facet>

::= (access read-write | read-only | initialize-only)


<propagation-facet> ::= (propagation inherit | no-inherit)


<source-facet> ::= (source exclusive | composite)


<pattern-match-facet>

::= (pattern-match reactive | non-reactive)


<visibility-facet> ::= (visibility private | public)


<create-accessor-facet>

::= (create-accessor ?NONE | read | write | read-write)


<override-message-facet>

::= (override-message ?DEFAULT | <message-name>)

<handler-documentation>

::= (message-handler <name> [<handler-type>])


<handler-type> ::= primary | around | before | after

Defmessage-handler Construct


<defmessage-handler-construct>

::= (defmessage-handler <class-name>

<message-name> [<handler type>] [<comment>]

(<parameter>* [<wildcard-parameter>])

<action>*)


<handler-type> ::= around | before | primary | after


<parameter> ::= <single-field-variable>


<wildcard-parameter> ::= <multifield-variable>

Definstances Construct


<definstances-construct>

::= (definstances <definstances-name>

[active] [<comment>]

<instance-template>*)


<instance-template> ::= (<instance-definition>)


<instance-definition> ::= <instance-name-expression> of
<class-name-expression>
<slot-override>*


<slot-override> ::= (<slot-name-expression> <expression>*)

Defmodule Construct


<defmodule-construct> ::= (defmodule <module-name> [<comment>]

<port-specification>*)


<port-specification> ::= (export <port-item>) |

(import <module-name> <port-item>)


<port-item> ::= ?ALL |

?NONE |

<port-construct> ?ALL |

<port-construct> ?NONE |

<port-construct> <construct-name>+


<port-construct> ::= deftemplate | defclass |

defglobal | deffunction |

defgeneric

Constraint Attributes


<constraint-attribute>

::= <type-attribute> |

<allowed-constant-attribute> |

<range-attribute> |

<cardinality-attribute>

<type-attribute> ::= (type <type-specification>)


<type-specification> ::= <allowed-type>+ | ?VARIABLE


<allowed-type> ::= SYMBOL | STRING | LEXEME |

INTEGER | FLOAT | NUMBER |

INSTANCE-NAME | INSTANCE-ADDRESS |

INSTANCE | EXTERNAL-ADDRESS |

FACT-ADDRESS


<allowed-constant-attribute>

::= (allowed-symbols <symbol-list>) |

(allowed-strings <string-list>) |

(allowed-lexemes <lexeme-list> |

(allowed-integers <integer-list>) |

(allowed-floats <float-list>) |

(allowed-numbers <number-list>) |

(allowed-instance-names <instance-list>) |

(allowed-values <value-list>)


<symbol-list> ::= <symbol>+ | ?VARIABLE


<string-list> ::= <string>+ | ?VARIABLE


<lexeme-list> ::= <lexeme>+ | ?VARIABLE


<integer-list> ::= <integer>+ | ?VARIABLE


<float-list> ::= <float>+ | ?VARIABLE


<number-list> ::= <number>+ | ?VARIABLE


<instance-name-list> ::= <instance-name>+ | ?VARIABLE


<value-list> ::= <constant>+ | ?VARIABLE


<range-attribute> ::= (range <range-specification>

<range-specification>)


<range-specification> ::= <number> | ?VARIABLE


<cardinality-attribute>

::= (cardinality <cardinality-specification>

<cardinality-specification>)


<cardinality-specification>

::= <integer> | ?VARIABLE


Appendix I   Reserved Function Names

This appendix lists all of the functions provided by either standard CLIPS or various CLIPS extensions. They should be considered reserved function names, and users should not create user defined functions with any of these names.


!=

*

**

+

-

/

<

<>

=

=

abs

acos

acosh

acot

acoth

acsc

acsch

active duplicate instance

active-initialize-instance

active-make-instance

active message duplicate instance

active-message-modify-instance

active-modify-instance

agenda

and

any-instancep

apropos

asec

asech

asin

asinh

assert

assert-string

atan

atanh

batch

batch*

bind

bload

bload-instances

break

browse-classes

bsave

bsave-instances

build

call-next-handler

call-next-method

call-specific-method

class

class-abstractp

class-existp

class-reactivep

class-slots

class-subclasses

class-superclasses

clear

clear-focus-stack

close

conserve-mem

constructs-to-c

cos

cosh

cot

coth

create$

csc

csch

defclass-module

deffacts-module

deffunction-module

defgeneric-module

defglobal-module

definstances-module

defrule-module

deftemplate-module

deg-grad

deg-rad

delayed-do-for-all-instances

delete$

delete-instance

dependencies

dependents

describe-class

direct-mv-delete

direct-mv-insert

direct-mv-replace

div

do-for-all-instances

do-for-instance

dribble-off

dribble-on

duplicate

duplicate-instance

duplicate-instance

dynamic-get

dynamic-put

edit

eq

eval

evenp

exit

exp

expand$

explode$

fact-existp

fact-index

fact-relation

fact-slot-names

fact-slot-value

facts

fetch

find-all-instances

find-instance

first$

float

floatp

focus

format

gensym

gensym*

get

get-auto-float-dividend

get-current-module

get-defclass-list

get-deffacts-list

get-deffunction-list

get-defgeneric-list

get-defglobal-list

get-definstances-list

get-defmessage-handler-list

get-defmethod-list

get-defmodule-list

get-defrule-list

get-deftemplate-list

get-dynamic-constraint-checking

get-fact-duplication

get-fact-list

get-focus

get-focus-stack

get-function-restrictions

get-incremental-reset

get-method-restrictions

get-reset-globals

get-salience-evaluation

get-sequence-operator-recognition

get-static-constraint-checking

get-strategy

grad-deg

halt

help

help-path

if

implode$

init-slots

initialize-instance

initialize-instance

insert$

instance-address

instance-addressp

instance-existp

instance-name

instance-name-to-symbol

instance-namep

instancep

instances

integer

integerp

length

length$

lexemep

list-defclasses

list-deffacts

list-deffunctions

list-defgenerics

list-defglobals

list-definstances

list-defmessage-handlers

list-defmethods

list-defmodules

list-defrules

list-deftemplates

list-focus-stack

list-watch-items

load

load*

load-facts

load-instances

log

log10

loop-for-count

lowcase

make-instance

make-instance

matches

max

mem-requests

mem-used

member

member$

message-duplicate-instance

message-duplicate-instance

message-handler-existp

message-modify-instance

message-modify-instance

min

mod

modify

modify-instance

modify-instance

multifieldp

mv-append

mv-delete

mv-replace

mv-slot-delete

mv-slot-insert

mv-slot-replace

mv-subseq

neq

next-handlerp

next-methodp

not

nth

nth$

numberp

object-pattern-match-delay

oddp

open

options

or

override-next-handler

override-next-method

pi

pointerp

pop-focus

ppdefclass

ppdeffacts

ppdeffunction

ppdefgeneric

ppdefglobal

ppdefinstances

ppdefmessage-handler

ppdefmethod

ppdefmodule

ppdefrule

ppdeftemplate

ppinstance

preview-generic

preview-send

primitives-info

print-region

printout

progn

progn$

put

rad-deg

random

read

readline

refresh

refresh-agenda

release-mem

remove

remove-break

rename

replace$

reset

rest$

restore-instances

retract

return

round

rule-complexity

rules

run

save

save-facts

save-instances

sec

sech

seed

send

sequencep

set-auto-float-dividend

set-break

set-current-module

set-dynamic-constraint-checking

set-fact-duplication

set-incremental-reset

set-reset-globals

set-salience-evaluation

set-sequence-operator-recognition

set-static-constraint-checking

set-strategy

setgen

show-breaks

show-defglobals

show-fht

show-fpn

show-joins

show-opn

sin

sinh

slot allowed values

slot-cardinality

slot-delete$

slot-direct-accessp

slot-direct-delete$

slot-direct-insert$

slot-direct-replace$

slot-existp

slot-facets

slot-initablep

slot-insert$

slot-publicp

slot-range

slot-replace$

slot-sources

slot-types

slot-writablep

sqrt

str-assert

str-cat

str-compare

str-explode

str-implode

str-index

str-length

stringp

sub-string

subclassp

subseq$

subset

subsetp

superclassp

switch

sym-cat

symbol-to-instance-name

symbolp

system

tan

tanh

time

toss

type

type

undefclass

undeffacts

undeffunction

undefgeneric

undefglobal

undefinstances

undefmessage-handler

undefmethod

undefrule

undeftemplate

unmake-instance

unwatch

upcase

watch

while

wordp

Appendix J   Bibliography of CLIPS Publications

Programming


Giarratano, J., and Riley, G. Expert Systems: Principles and Programming, 3rd Edition, Boston, PWS Publishing Company, 1998.


Gonzalez, A. J., and Dankel, D. D. Engineering of Knowledge-basedSystems: Theory and Practice, Prentice Hall, 1993.


Jackson, P. Introduction to Expert Systems, 3rd Edition, Reading, Addison-Wesley, 1998.

Reviews


Brooke, T. “The Art of Production Systems,” AI Expert, January 1992.


Brooke, T. “Software Review,” AI Expert, April 1988.


Golden, J. “Shell Review Monthly,” AI Today, March/April 1988.


Mettrey, W. “A Comparative Evaluation of Expert System Tools,” Computer, February 1991.


Popolizio, J. “CLIPS: NASA’s COSMIC Shell,” Artificial Intelligence Research, August 1, 1988.


Raeth, P. “Two PC–based Expert System Shells for the First–time Developer,” Computer, November 1988.

Overviews


Culbert, C., et al., “A Solution to the Expert System Delivery Problem,” Proceedings of the ISA/88, Houston, TX, October 1988.


Riley, G. “C Language Integrated Production System,” in Encyclopedia of Computer Science and Technology, Volume 37. Edited by A. Kent and J.G. Williams. New York, Marcel Dekker, Inc., 1997.


Riley, G. “Expert Systems Methodology,” in The Industrial Electronics Handbook. Edited by J.D. Irwin. Boca Raton, CRC Press, 1997.


Riley, G. “CLIPS: An Expert System Building Tool,” Proceedings of the Technology 2001 Conference, San Jose, CA, December 1991.


Riley, G. “CLIPS: A Tool for the Development and Delivery of Expert Systems,” Proceedings of the Technology 2000 Conference, Washington, DC, November 1990.


Riley G., and Donnell, B. “Advanced CLIPS Capabilities,” Proceedings of The Fourth Annual Workshop on Space Operations Applications and Research (SOAR ’90), Albuquerque, NM, June 1990.


Riley, G., et al. “CLIPS: An Expert System Tool for Training, Development, and Delivery,” in Intelligent Systems Review, Volume 1, Number 1, Fall 1988.


Riley, G., et al., “CLIPS: An Expert System Tool for Delivery and Training,” Proceedings of the Third Conference on Artificial Intelligence for Space Applications, Huntsville, AL, November 1987.

Applications


Carreno, L. A. and Steel, R. A. “Life Insurance Risk Assessment using a Fuzzy Logic Expert System,” Proceedings of the North American Fuzzy Logic Processing Society (NAFIPS 1992), Houston, TX, December 1992.


Cheatham, J. B., et al. “A Multi–Sensor System for Robotics Proximity Operations,” Proceedings of The Second Annual Workshop on Space Operations Automation and Robotics (SOAR ’88), Albuquerque, NM, July 1988.


Chen, Y. “Applying Knowledge–Based Expert System to Meat Grading,” Proceedings of The Annual AI Systems in Government Conference, Washington, D.C., March 1989.


“CLIPS: A NASA Developed Expert System Tool,” NASA Tech Briefs, November/December 1987.


Dutton, T. “HUB SIAASHING: A Knowledge–Based System for Severe, Temporary Airline Schedule Reduction,” Innovative Applications of Artificial Intelligence 4, Klahr, Philip, and Scott, A. Carlisle ed., 1992.


Ehler, G. B. “A Multiple Knowledge-Based Spatial Decision Support System for Industrial Site Selection,” M.S. Thesis, Department of Geography, University of South Carolina, Columbia, SC.


Fink, P., and Herren, L. T. “An Intelligent Tutoring System to Teach Interdependent Cognitive and High Performance Skills,” Proceedings of Contributed Sessions 1991 Conference on Intelligent Computer Aided Training, Houston, TX, November 1991.


Fink, P. “NESSUS/EXPERT: Bridging the Gap between Artificial Intelligence and FORTRAN,” Proceedings of The Second Annual Workshop on Space Operations Automation and Robotics (SOAR ’88), Albuquerque, NM, July 1988.


Flamm, R. O., et al. “The Integrated Southern Pine Beetle Expert System: ISPBEX,” Expert Systems with Applications, Vol. 2, 1991.


Franier, R., et al. “PI–in–a–Box: A Knowledge–based System for Space Science Experimentation,” Proceedings of the Fifth Innovative Applications of Artificial Intelligence Conference, July 11–15, 1993, Washington, D.C.


Frainier, R., et al. “PI-in-a-Box: A Knowledge-Based System for Space Science Experimentation,” AI magazine, Volume 15, No. 1, Spring, 1994.


Frainier, R., et al. “PI in the Sky: The Astronaut Science Advisor on SLS-2,” Proceedings of The Seventh Annual Workshop on Space Operations Applications and Research (SOAR ’93), Houston, TX, August 1993.


Germain, D., and Desrosiers, S. “Turning Up the Heat on Space Station Training: The Active Thermal Control System ICAT,” Proceedings of Contributed Sessions 1991 Conference on Intelligent Computer Aided Training, Houston, TX, November 1991.


Grinstein, G. G., et al. “Virtual Environment Architecture for Rapid Application Development,” Proceedings of The Contributed Sessions 1993 Conference on Intelligent Computer Aided Training and Virtual Environment Technology (ICAT-VET ’93), Houston, TX, May 1993.


Haymann–Haber, G., et al. “An Expert System to Advise Astronauts During Experiments: The Protocol Manager Module,” Proceedings of The Third Annual Workshop on Space Operations Automation and Robotics (SOAR ’89), Houston, TX, July 1989.


Hill, T., and Faltisco, R. “Intelligent Fault Management for the Space Station Active Thermal Control System,” Proceedings of The Fifth Annual Workshop on Space Operations Applications and Research (SOAR ’91), Houston, TX, July 1991.


Hipwell, D. P. “Developing Realistic Cooperative Behaviors for Autonomous Agents in Air Combat Simuation,” M.S. Thesis, Air Force Institute of Technology, Wright Patternson AFB, Ohio, 1993.


Hughes, P. M. “CLEAR: Automating Control Centers with Expert System Technology,” Proceedings of The Third Annual Workshop on Space Operations Automation and Robotics (SOAR ’89), Houston, TX, July 1989.


Johnson, W. B., et al. “An Intelligent Tutoring System for Space Shuttle Diagnosis,” Proceedings of The Second Annual Workshop on Space Operations Automation and Robotics (SOAR ’88), Albuquerque, NM, July 1988.


Kahn, M. G., et al. “An Expert System for Culture-Based Infection Control Surveillance,” Proceedings of The Seventeenth Annual Symposium on Computer Applications in Medical Care (SCAMC ’93), Washington, D.C., October 1993.


Kingston, J. “Pragmatic KADS: A methodological approach to a small knowledge based systems project,” Expert Systems: The International Journal of Knowledge Engineering, 4, 4, November 1992.


Kosta, C. P., and Krolak, P. D. “Rapid Prototyping 3D Virtual World Interfaces within a Virtual Factory Environment,” Proceedings of The Contributed Sessions 1993 Conference on Intelligent Computer Aided Training and Virtual Environment Technology (ICAT-VET ’93), Houston, TX, May 1993.


Kosta, C. P., and Krolak, P. D. “An Artificial Reality Environment for Remote Factory Control and Monitoring,” Vision 21: Interdisciplinary Science and Engineering in the Era of Cyberspace, NASA/Lewis Research Center, December 1993.


Kovarik, V. J. “Autonomously Acquiring Declarative and Procedural Domain Knowledge for ICAT Systems,” Proceedings of The Contributed Sessions 1993 Conference on Intelligent Computer Aided Training and Virtual Environment Technology (ICAT-VET ’93), Houston, TX, May 1993.


Lauriente, M., et al. “Diagnosing Anomalies of Spacecraft for Space Maintenance and Servicing,” Proceedings of The Seventh Annual Workshop on Space Operations Applications and Research (SOAR ’93), Houston, TX, August 1993.


Lee, L., and Hill, R. W., “Process Control and Recovery in the Link Monitor and Control Operator Assistant,” Proceedings of The Sixth Annual Workshop on Space Operations Applications and Research (SOAR ’92), Houston, TX, August 1992.


Leinweber, D. “Finance,” Expert Systems and Artificial Intelligence: Applications and Management, Howard W. Sams & Company, Bartee, T. C. ed., 1988.


Loftin, K. C., et al. “The Application of Integrated Knowledge–Based Systems for the Biomedical Risk Accessment Intelligent Network (BRAIN),” Proceedings of Technology 2002: The Third National Technology Transfer Conference and Exposition, Washington D.C., February 1993.


Loftin, R. B., and Savely, R.T. “Intelligent Computer Aided Training and Tutoring,” Proceedings of the Technology 2000 Conference, Washington, DC, November 1990.


Loftin, R. B., et al. “An Intelligent Training System for Space Shuttle Flight Controllers,” Innovative Applications of Artificial Intelligence, 1989, AAAI Press/The MIT Press, Menlo Press, Schoor, Herbert, and Rappaport, Alain ed.


Loftin, R. B., et al. “An Intelligent Training System for Payload–Assist Module Deploys,” Proceedings of The First Annual Workshop on Space Operations Automation and Robotics (SOAR ’87), Houston, TX, August 1987.


Lucas, T. S., and Lewis, G. “DISPLAVAL: An Expert System Approach for the Training of Display Builders,” Proceedings of Contributed Sessions 1991 Conference on Intelligent Computer Aided Training, Houston, TX, November 1991.


McCarthy, L., et al. “Spatial Considerations for Instructional Development in a Virtual Environment,” Proceedings of The Contributed Sessions 1993 Conference on Intelligent Computer Aided Training and Virtual Environment Technology (ICAT-VET ’93), Houston, TX, May 1993.


“Mission Accomplished,” NASA Tech Briefs, September 1993.


Mitchell, P. “An Expert System for Shuttle and Satellite Radar Tracker Scheduling,” Proceedings of The Second Annual Workshop on Space Operations Automation and Robotics (SOAR ’88), Albuquerque, NM, July 1988.


Mitchell, R. “Expert Systems and Air–Combat Simulation,” AI Expert, September 1989.


Mortenson, P. “Predicting Wind Shear from the Dispatch Office,” Airline Executive, April 1988.


Mueller, S. “Development of a Personal–Computer–Based Intelligent Tutoring System,” Proceedings of The Second Annual Workshop on Space Operations Automation and Robotics (SOAR ’88), Albuquerque, NM, July 1988.


Muratore, J., et al. “Space Shuttle Telemetry Monitoring,” Innovative Applications of Artificial Intelligence, 1989, AAAI Press/The MIT Press, Menlo Press, Schoor, Herbert, and Rappaport, Alain ed.


Nash, J. “Expert Systems: A New Partnership,” AI Expert, December 1992.


Norton, J. E., et al. “Microcomputer Intelligence for Technical Training (MITT): The Evolution of an Intelligent Tutoring System,” Proceedings of Contributed Sessions 1991 Conference on Intelligent Computer Aided Training, Houston, TX, November 1991.


Proceedings of the First CLIPS Conference, Houston, Texas, August 1990.


Proceedings of the Second CLIPS Conference, Houston, Texas, September 1991.


Proceedings of the Third CLIPS Conference, Houston, Texas, September 1994.


Robey, B., et al. “The DRAIR Advisor: A Knowledge–Based System for Materiel Deficiency Analysis,” Proceedings of the Fifth Innovative Applications of Artificial Intelligence Conference, July 11–15, 1993, Washington, D.C.


Robey, B., et al. “DRAIR Advisor: A Knowledge-Based System for Materiel-Deficiency Analysis,” AI magazine, Volume 15, No. 2, Summer, 1994.


Rolincik, M, et al. “An On–line Expert System for Diagnosing Environmentally Induced Spacecraft Anomalies using CLIPS,” Proceedings of The Sixth Annual Workshop on Space Operations Applications and Research (SOAR ’92), Houston, TX, August 1992.


Rolincik, M., et al. “An Expert System for Diagnosing Environmentally Induced Spacecraft Anomolies,” Proceedings of The Fifth Annual Workshop on Space Operations Applications and Research (SOAR ’91), Houston, TX, July 1991.


Saito, T., et al. “Acquiring Knowledge within an ICAT (Intelligent Computer–Aided Training) Environment: Factors and Issues,” Proceedings of Contributed Sessions 1991 Conference on Intelligent Computer Aided Training, Houston, TX, November 1991.


Saito, T., et al. “On the Acquisition and Representation of Procedural Knowledge,” Proceedings of The Fifth Annual Workshop on Space Operations Applications and Research (SOAR ’91), Houston, TX, July 1991.


Scholtz, T. “The State Transition Diagram with Path Priority and it’s Applications,” M.S. Thesis, Naval Postgraduate School, Monterey, CA, September 1993.


Schultz, R. D, and Stobie, I. “The AI Bus Architecture for Distributed Knowledge–Based Systems,” Proceedings of The Fourth Annual Workshop on Space Operations Applications and Research (SOAR ’90), Albuquerque, NM, June 1990.


Spelt, P. F. “Learning by an Autonomous Robot at a Process Control Panel,” IEEE Expert, Winter 1989.


Spinoff 1993, NASA, pp. 88, 102, 120–121, 1994.


Spinoff 1992, NASA, p. 121, 1993.


Spinoff 1991, NASA, pp. 110–111, 1992.


Swartz, M., et al. “Intelligent Help for Radar Maintenance Troubleshooters,” Proceedings of Contributed Sessions 1991 Conference on Intelligent Computer Aided Training, Houston, TX, November 1991.


Szatkowski, G. P., and Levin, B. E. “Expert System Decision Support for Low–cost Launch Vehicle Operations,” Proceedings of The Fourth Annual Workshop on Space Operations Applications and Research (SOAR ’90), Albuquerque, NM, June 1990.


Truszkowski, W. “Advances in Knowledge–Based Software Engineering,” Proceedings of the Technology 2001Conference, San Jose, CA, December 1991.


Wallfesh, S. K. “Infantry Load Planning with LES,” Artificial Intelligence Applications for Logistics, Aerospace Systems, Robotics & Personnel, American Defense Preparedness Association, WIlliamsburg, VA, 8–10 March 1993.


Wang, L., and Bochsler, D. “Space Shuttle Onboard Navigation Console Expert/Trainer System,” Proceedings of The First Annual Workshop on Space Operations Automation and Robotics (SOAR ’87), Houston, TX, August 1987.


Warren, K. C., and Goodman, B. A. “Engineering Intelligent Tutoring Systems,” Proceedings of The Contributed Sessions 1993 Conference on Intelligent Computer Aided Training and Virtual Environment Technology (ICAT-VET ’93), Houston, TX, May 1993.


Wiederholt, B. J. “MITT Writer: An Authoring System for Developing Intelligent Tutors for Complex Technical Domains,” Proceedings of Contributed Sessions 1991 Conference on Intelligent Computer Aided Training, Houston, TX, November 1991.


Woods, D. “Space Station Freedom: Embedding AI,” AI Expert, April 1992.

Enhancements/Implementation


Donnell, B., “Object/rule Integration in CLIPS,” Expert Systems: The International Journal of Knowledge Engineering and Neural Networks, Learned Information, New Jersey, February 1994, Vol. 11, No. 1, ISSN 0266-4720, pp. 29-45.


Franke, J. L., et al. “A General Purpose Certainty Processing Extension to CLIPS,” Proceedings of The 7th Florida Artificial Intelligence Research Symposium, Florida AI Research Society, 1994.


Le, T., and Homeier, P. “Portable Inference Engine: An Extended CLIPS for Real–Time Production Systems,” Proceedings of The Second Annual Workshop on Space Operations Automation and Robotics (SOAR ’88), Albuquerque, NM, July 1988.


Li, Y. P. “DCLIPS—A Distributed CLIPS Implementation,” Proceedings of the 9th AIAA Computing in Aerospace Conference, American Institute of Aeronautics and Astronautics, San Diego, CA, October 1993.


Odette, L. L., Intelligent Embedded Systems, Addison–Wesley Publishing Company, pp. 63–110, 1991.


Riley, G. “Implementing CLIPS on a Parallel Computer,” Proceedings of The First Annual Workshop on Space Operations Automation and Robotics (SOAR ’87), Houston, TX, August 1987.


Riley, G. “Implementation of an Expert System Shell on a Parallel Computer,” Proceedings of The Third Annual Artificial Intelligence & Advanced Computer Technology Conference, Long Beach Convention Center, Long Beach, CA, April 1987.


Salzgeber, M. J., et al. “Managing Uncertainty in CLIPS: A System Level Approach,” Proceedings of The 6th Florida Artificial Intelligence Research Symposium, Florida AI Research Society, 1993.


Eick, C. F., et al. “DALI—A Knowledge Base Management System,” Proceedings of the 1st Conference on Industrial and Engineering Applications of AI & Expert Systems.

Rete Pattern Matching Algorithm


Forgy, C. “Rete: A Fast Algorithm for the Many Pattern/Many Object Pattern Match Problem,” Artificial Intelligence, 19, pp. 17–37, 1982.


Forgy, C. “On the Efficient Implementation of Production Systems,” Ph. D. Thesis, Carnegie Mellon University, 1979.


Schneier, B. “The Rete Matching Algorithm,” AI Expert, pp. 24-29, December 1992.

 
 
clips/bpg.txt · Last modified: 2010/01/05 02:09 by admin
topheader
© 1998-2019, SciOS Scientific Operating Systems GmbH

Legal | Credits | Profile | Contact | Customer Login