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+<HTML>
+<HEAD>
+<META HTTP-EQUIV="Content-Type" Content="text/html; charset=Windows-1252">
+<TITLE>DEFMESSAGE HANDLER</TITLE>
+</HEAD>
+<BODY BGCOLOR="#FFFFFF" TEXT="#000000">
+<OBJECT TYPE="application/x-oleobject" CLASSID="clsid:1e2a7bd0-dab9-11d0-b93a-00c04fc99f9e">
+	<PARAM NAME="Keyword" VALUE="DEFMESSAGE-HANDLER">
+</OBJECT>
+<H1><A NAME="defmessage_handler"></A>DEFMESSAGE HANDLER</H1>
+<P></P>
+<P>Objects are manipulated by sending them messages via the function send.  The </P>
+<P>result of a message is a useful return-value or side-effect.  A </P>
+<P>defmessage-handler is a construct for specifying the behavior of a class of </P>
+<P>objects in response to a particular message.  The implementation of a message </P>
+<P>is made up of pieces of procedural code called message-handlers (or handlers </P>
+<P>for short).  Each class in the class precedence list of an object's class can </P>
+<P>have handlers for a message.  In this way, the object's class and all its </P>
+<P>superclasses share the labor of handling the message.  Each class's handlers </P>
+<P>handle the part of the message which is appropriate to that class.  Within a </P>
+<P>class, the handlers for a particular message can be further subdivided into </P>
+<P>four types or categories: primary, before, after and around.</P>
+<P>A defmessage-handler is comprised of seven elements: 1) a class name to which </P>
+<P>to attach the handler (the class must have been previously defined), 2) a </P>
+<P>message name to which the handler will respond, 3) an optional type (the </P>
+<P>default is primary), 4) an optional comment, 5) a list of parameters that will</P>
+<P>be passed to the handler during execution, 6) an optional wildcard parameter </P>
+<P>and 7) a series of expressions which are executed in order when the handler </P>
+<P>is called.  The return-value of a message-handler is the evaluation of the last </P>
+<P>expression in the body.</P>
+<P>The syntax of the defmessage-handler construct is:</P>
+<P></P>
+<PRE><CODE>(defmessage-handler &lt;class-name&gt; &lt;message-name&gt;
+   [&lt;handlertype&gt;] [&lt;comment&gt;]
+   (&lt;parameter&gt;* [&lt;wildcard-parameter&gt;])
+   &lt;action&gt;*)
+&lt;handler-type&gt;       ::= around | before | primary | after
+&lt;parameter&gt;          ::= &lt;single-field-variable&gt;
+&lt;wildcard-parameter&gt; ::= &lt;multifield-variable&gt;</CODE></PRE>
+</BODY>
+</HTML>