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<TITLE>CLHS: Section 3.1.2.1.2.2</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="03_ababa.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Previous]" SRC="../Graphics/Prev.gif" ALIGN=Bottom></A><A REL=UP HREF="03_abab.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Up]" SRC="../Graphics/Up.gif" ALIGN=Bottom></A><A REL=NEXT HREF="03_ababc.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Next]" SRC="../Graphics/Next.gif" ALIGN=Bottom></A></H1>
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<H2>
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3.1.2.1.2.2 Macro Forms</H2> <P>
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If the <A REL=DEFINITION HREF="26_glo_o.htm#operator"><I>operator</I></A> names a <A REL=DEFINITION HREF="26_glo_m.htm#macro"><I>macro</I></A>, its associated <A REL=DEFINITION HREF="26_glo_m.htm#macro_function"><I>macro function</I></A> is applied to the entire <A REL=DEFINITION HREF="26_glo_f.htm#form"><I>form</I></A> and the result of that application is used in place of the original <A REL=DEFINITION HREF="26_glo_f.htm#form"><I>form</I></A>. <P>
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Specifically, a <A REL=DEFINITION HREF="26_glo_s.htm#symbol"><I>symbol</I></A> names a <A REL=DEFINITION HREF="26_glo_m.htm#macro"><I>macro</I></A> in a given <A REL=DEFINITION HREF="26_glo_l.htm#lexical_environment"><I>lexical environment</I></A> if <A REL=DEFINITION HREF="f_macro_.htm#macro-function"><B>macro-function</B></A> is <A REL=DEFINITION HREF="26_glo_t.htm#true"><I>true</I></A> of the <A REL=DEFINITION HREF="26_glo_s.htm#symbol"><I>symbol</I></A> and that <A REL=DEFINITION HREF="26_glo_e.htm#environment"><I>environment</I></A>. The <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>function</I></A> returned by <A REL=DEFINITION HREF="f_macro_.htm#macro-function"><B>macro-function</B></A> is a <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>function</I></A> of two arguments, called the expansion function. The expansion function is invoked by calling the <A REL=DEFINITION HREF="26_glo_m.htm#macroexpand_hook"><I>macroexpand hook</I></A> with the expansion function as its first argument, the entire <A REL=DEFINITION HREF="26_glo_m.htm#macro_form"><I>macro form</I></A> as its second argument, and an <A REL=DEFINITION HREF="26_glo_e.htm#environment_object"><I>environment object</I></A> (corresponding to the current <A REL=DEFINITION HREF="26_glo_l.htm#lexical_environment"><I>lexical environment</I></A>) as its third argument. The <A REL=DEFINITION HREF="26_glo_m.htm#macroexpand_hook"><I>macroexpand hook</I></A>, in turn, calls the expansion function with the <A REL=DEFINITION HREF="26_glo_f.htm#form"><I>form</I></A> as its first argument and the <A REL=DEFINITION HREF="26_glo_e.htm#environment"><I>environment</I></A> as its second argument. The <A REL=DEFINITION HREF="26_glo_v.htm#value"><I>value</I></A> of the expansion function, which is passed through by the <A REL=DEFINITION HREF="26_glo_m.htm#macroexpand_hook"><I>macroexpand hook</I></A>, is a <A REL=DEFINITION HREF="26_glo_f.htm#form"><I>form</I></A>. The returned <A REL=DEFINITION HREF="26_glo_f.htm#form"><I>form</I></A> is <I>evaluated</I> in place of the original <A REL=DEFINITION HREF="26_glo_f.htm#form"><I>form</I></A>. <P>
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The consequences are undefined if a <A REL=DEFINITION HREF="26_glo_m.htm#macro_function"><I>macro function</I></A> destructively modifies any part of its <A REL=DEFINITION HREF="26_glo_f.htm#form"><I>form</I></A> argument. <P>
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A <A REL=DEFINITION HREF="26_glo_m.htm#macro_name"><I>macro name</I></A> is not a <A REL=DEFINITION HREF="26_glo_f.htm#function_designator"><I>function designator</I></A>, and cannot be used as the <I>function</I> argument to <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>functions</I></A> such as <A REL=DEFINITION HREF="f_apply.htm#apply"><B>apply</B></A>, <A REL=DEFINITION HREF="f_funcal.htm#funcall"><B>funcall</B></A>, or <A REL=DEFINITION HREF="f_map.htm#map"><B>map</B></A>. <P>
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An <A REL=DEFINITION HREF="26_glo_i.htm#implementation"><I>implementation</I></A> is free to implement a Common Lisp <A REL=DEFINITION HREF="26_glo_s.htm#special_operator"><I>special operator</I></A> as a <A REL=DEFINITION HREF="26_glo_m.htm#macro"><I>macro</I></A>. An <A REL=DEFINITION HREF="26_glo_i.htm#implementation"><I>implementation</I></A> is free to implement any <A REL=DEFINITION HREF="26_glo_m.htm#macro"><I>macro</I></A> <A REL=DEFINITION HREF="26_glo_o.htm#operator"><I>operator</I></A> as a <A REL=DEFINITION HREF="26_glo_s.htm#special_operator"><I>special operator</I></A>, but only if an equivalent definition of the <A REL=DEFINITION HREF="26_glo_m.htm#macro"><I>macro</I></A> is also provided. <P>
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The next figure lists some <A REL=DEFINITION HREF="26_glo_d.htm#defined_name"><I>defined names</I></A> that are applicable to <A REL=DEFINITION HREF="26_glo_m.htm#macro"><I>macros</I></A>. <P>
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<PRE>
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<A REL=DEFINITION HREF="v_mexp_h.htm#STmacroexpand-hookST">*macroexpand-hook*</A> <A REL=DEFINITION HREF="f_macro_.htm#macro-function">macro-function</A> <A REL=DEFINITION HREF="f_mexp_.htm#macroexpand-1">macroexpand-1</A>
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<A REL=DEFINITION HREF="m_defmac.htm#defmacro">defmacro</A> <A REL=DEFINITION HREF="f_mexp_.htm#macroexpand">macroexpand</A> <A REL=DEFINITION HREF="s_flet_.htm#macrolet">macrolet</A>
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</PRE>
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<P><B>Figure 3-3. Defined names applicable to macros</B> <P>
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<P><HR>The following <A REL=META HREF="../Front/X3J13Iss.htm">X3J13 cleanup issue</A>, <I>not part of the specification</I>, applies to this section:<P><UL><LI> <A REL=CHILD HREF="../Issues/iss301.htm">SELF-MODIFYING-CODE:FORBID</A><P></UL><HR>
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