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80 lines
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<!-- Common Lisp HyperSpec (TM), version 7.0 generated by Kent M. Pitman on Mon, 11-Apr-2005 2:31am EDT -->
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<TITLE>CLHS: Macro DEFINE-MODIFY-MACRO</TITLE>
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<H1><A REV=MADE HREF="http://www.lispworks.com/"><IMG WIDTH=80 HEIGHT=65 ALT="[LISPWORKS]" SRC="../Graphics/LWSmall.gif" ALIGN=Bottom></A><A REL=TOP HREF="../Front/index.htm"><IMG WIDTH=237 HEIGHT=65 ALT="[Common Lisp HyperSpec (TM)]" SRC="../Graphics/CLHS_Sm.gif" ALIGN=Bottom></A> <A REL=PREV HREF="s_progn.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Previous]" SRC="../Graphics/Prev.gif" ALIGN=Bottom></A><A REL=UP HREF="c_data_a.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Up]" SRC="../Graphics/Up.gif" ALIGN=Bottom></A><A REL=NEXT HREF="m_defset.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Next]" SRC="../Graphics/Next.gif" ALIGN=Bottom></A></H1>
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<A NAME="define-modify-macro"><I>Macro</I> <B>DEFINE-MODIFY-MACRO</B></A> <P>
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<P><B>Syntax:</B><P>
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<P>
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<B>define-modify-macro</B> <I>name lambda-list function [documentation]</I> => <I>name</I><P>
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<P>
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<P><B>Arguments and Values:</B><P>
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<P>
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<I>name</I>---a <A REL=DEFINITION HREF="26_glo_s.htm#symbol"><I>symbol</I></A>. <P>
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<I>lambda-list</I>---a <A REL=DEFINITION HREF="26_glo_d.htm#define-modify-macro_lambda_list"><I>define-modify-macro lambda list</I></A> <P>
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<I>function</I>---a <A REL=DEFINITION HREF="26_glo_s.htm#symbol"><I>symbol</I></A>. <P>
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<I>documentation</I>---a <A REL=DEFINITION HREF="26_glo_s.htm#string"><I>string</I></A>; not evaluated. <P>
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<P><B>Description:</B><P>
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<P>
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<A REL=DEFINITION HREF="#define-modify-macro"><B>define-modify-macro</B></A> defines a <A REL=DEFINITION HREF="26_glo_m.htm#macro"><I>macro</I></A> named <I>name</I> to <A REL=DEFINITION HREF="26_glo_r.htm#read"><I>read</I></A> and <A REL=DEFINITION HREF="26_glo_w.htm#write"><I>write</I></A> a <A REL=DEFINITION HREF="26_glo_p.htm#place"><I>place</I></A>. <P>
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The arguments to the new <A REL=DEFINITION HREF="26_glo_m.htm#macro"><I>macro</I></A> are a <A REL=DEFINITION HREF="26_glo_p.htm#place"><I>place</I></A>, followed by the arguments that are supplied in <I>lambda-list</I>. <A REL=DEFINITION HREF="26_glo_m.htm#macro"><I>Macros</I></A> defined with <A REL=DEFINITION HREF="#define-modify-macro"><B>define-modify-macro</B></A> correctly pass the <A REL=DEFINITION HREF="26_glo_e.htm#environment_parameter"><I>environment parameter</I></A> to <A REL=DEFINITION HREF="f_get_se.htm#get-setf-expansion"><B>get-setf-expansion</B></A>. <P>
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When the <A REL=DEFINITION HREF="26_glo_m.htm#macro"><I>macro</I></A> is invoked, <I>function</I> is applied to the old contents of the <A REL=DEFINITION HREF="26_glo_p.htm#place"><I>place</I></A> and the <I>lambda-list</I> arguments to obtain the new value, and the <A REL=DEFINITION HREF="26_glo_p.htm#place"><I>place</I></A> is updated to contain the result. <P>
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Except for the issue of avoiding multiple evaluation (see below), the expansion of a <A REL=DEFINITION HREF="#define-modify-macro"><B>define-modify-macro</B></A> is equivalent to the following: <P>
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<PRE>
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(defmacro name (reference . lambda-list)
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documentation
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`(setf ,reference
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(function ,reference ,arg1 ,arg2 ...)))
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</PRE>
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</TT> <P>
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where <I>arg1</I>, <I>arg2</I>, ..., are the parameters appearing in <I>lambda-list</I>; appropriate provision is made for a <A REL=DEFINITION HREF="26_glo_r.htm#rest_parameter"><I>rest parameter</I></A>. <P>
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The <A REL=DEFINITION HREF="26_glo_s.htm#subform"><I>subforms</I></A> of the macro calls defined by <A REL=DEFINITION HREF="#define-modify-macro"><B>define-modify-macro</B></A> are evaluated as specified in <A REL=CHILD HREF="05_aaa.htm">Section 5.1.1.1 (Evaluation of Subforms to Places)</A>. <P>
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<I>Documentation</I> is attached as a <A REL=DEFINITION HREF="26_glo_d.htm#documentation_string"><I>documentation string</I></A> to <I>name</I> (as kind <A REL=DEFINITION HREF="s_fn.htm#function"><B>function</B></A>) and to the <A REL=DEFINITION HREF="26_glo_m.htm#macro_function"><I>macro function</I></A>. <P>
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If a <A REL=DEFINITION HREF="#define-modify-macro"><B>define-modify-macro</B></A> <A REL=DEFINITION HREF="26_glo_f.htm#form"><I>form</I></A> appears as a <A REL=DEFINITION HREF="26_glo_t.htm#top_level_form"><I>top level form</I></A>, the <A REL=DEFINITION HREF="26_glo_c.htm#compiler"><I>compiler</I></A> must store the <A REL=DEFINITION HREF="26_glo_m.htm#macro"><I>macro</I></A> definition at compile time, so that occurrences of the macro later on in the file can be expanded correctly. <P>
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<P><B>Examples:</B><P>
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<PRE>
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(define-modify-macro appendf (&rest args)
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append "Append onto list") => APPENDF
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(setq x '(a b c) y x) => (A B C)
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(appendf x '(d e f) '(1 2 3)) => (A B C D E F 1 2 3)
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x => (A B C D E F 1 2 3)
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y => (A B C)
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(define-modify-macro new-incf (&optional (delta 1)) +)
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(define-modify-macro unionf (other-set &rest keywords) union)
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</PRE>
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</TT> <P>
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<P><B>Side Effects:</B><P>
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<P>
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A macro definition is assigned to <I>name</I>. <P>
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<P><B>Affected By:</B> None.
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<P>
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<P><B>Exceptional Situations:</B> None.
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<P>
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<P><B>See Also:</B><P>
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<P>
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<A REL=DEFINITION HREF="m_defset.htm#defsetf"><B>defsetf</B></A>, <A REL=DEFINITION HREF="m_defi_3.htm#define-setf-expander"><B>define-setf-expander</B></A>, <A REL=DEFINITION HREF="f_docume.htm#documentation"><B>documentation</B></A>, <A REL=CHILD HREF="03_dk.htm">Section 3.4.11 (Syntactic Interaction of Documentation Strings and Declarations)</A> <P>
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<P><B>Notes:</B> None.
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<P>
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<P><HR>The following <A REL=META HREF="../Front/X3J13Iss.htm">X3J13 cleanup issues</A>, <I>not part of the specification</I>, apply to this section:<P><UL><LI> <A REL=CHILD HREF="../Issues/iss059.htm">COMPILE-FILE-HANDLING-OF-TOP-LEVEL-FORMS:CLARIFY</A><LI> <A REL=CHILD HREF="../Issues/iss135.htm">DOCUMENTATION-FUNCTION-BUGS:FIX</A><LI> <A REL=CHILD HREF="../Issues/iss279.htm">PUSH-EVALUATION-ORDER:FIRST-ITEM</A><LI> <A REL=CHILD HREF="../Issues/iss308.htm">SETF-METHOD-VS-SETF-METHOD:RENAME-OLD-TERMS</A><LI> <A REL=CHILD HREF="../Issues/iss185.htm">GET-SETF-METHOD-ENVIRONMENT:ADD-ARG</A><P></UL><HR>
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