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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: Section 3.2.2.1</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_bb.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Previous]" SRC="../Graphics/Prev.gif" ALIGN=Bottom></A><A REL=UP HREF="03_bb.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Up]" SRC="../Graphics/Up.gif" ALIGN=Bottom></A><A REL=NEXT HREF="03_bbaa.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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3.2.2.1 Compiler Macros</H2> <P>
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A <A REL=DEFINITION HREF="26_glo_c.htm#compiler_macro"><I>compiler macro</I></A> can be defined for a <A REL=DEFINITION HREF="26_glo_n.htm#name"><I>name</I></A> that also names a <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>function</I></A> or <A REL=DEFINITION HREF="26_glo_m.htm#macro"><I>macro</I></A>. That is, it is possible for a <A REL=DEFINITION HREF="26_glo_f.htm#function_name"><I>function name</I></A> to name both a <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>function</I></A> and a <A REL=DEFINITION HREF="26_glo_c.htm#compiler_macro"><I>compiler macro</I></A>. <P>
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A <A REL=DEFINITION HREF="26_glo_f.htm#function_name"><I>function name</I></A> names a <A REL=DEFINITION HREF="26_glo_c.htm#compiler_macro"><I>compiler macro</I></A> if <A REL=DEFINITION HREF="f_cmp_ma.htm#compiler-macro-function"><B>compiler-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_f.htm#function_name"><I>function name</I></A> in the <A REL=DEFINITION HREF="26_glo_l.htm#lexical_environment"><I>lexical environment</I></A> in which it appears. Creating a <A REL=DEFINITION HREF="26_glo_l.htm#lexical_binding"><I>lexical binding</I></A> for the <A REL=DEFINITION HREF="26_glo_f.htm#function_name"><I>function name</I></A> not only creates a new local <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>function</I></A> or <A REL=DEFINITION HREF="26_glo_m.htm#macro"><I>macro</I></A> definition, but also <A REL=DEFINITION HREF="26_glo_s.htm#shadow"><I>shadows</I></A>[2] the <A REL=DEFINITION HREF="26_glo_c.htm#compiler_macro"><I>compiler macro</I></A>. <P>
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The <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>function</I></A> returned by <A REL=DEFINITION HREF="f_cmp_ma.htm#compiler-macro-function"><B>compiler-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. To expand a <A REL=DEFINITION HREF="26_glo_c.htm#compiler_macro"><I>compiler macro</I></A>, 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 compiler macro <A REL=DEFINITION HREF="26_glo_f.htm#form"><I>form</I></A> as its second argument, and the current compilation <A REL=DEFINITION HREF="26_glo_e.htm#environment"><I>environment</I></A> (or with the current lexical <A REL=DEFINITION HREF="26_glo_e.htm#environment"><I>environment</I></A>, if the <A REL=DEFINITION HREF="26_glo_f.htm#form"><I>form</I></A> is being processed by something other than <A REL=DEFINITION HREF="f_cmp_fi.htm#compile-file"><B>compile-file</B></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 return value from the expansion function, which is passed through by the <A REL=DEFINITION HREF="26_glo_m.htm#macroexpand_hook"><I>macroexpand hook</I></A>, might either be the <A REL=DEFINITION HREF="26_glo_s.htm#same"><I>same</I></A> <A REL=DEFINITION HREF="26_glo_f.htm#form"><I>form</I></A>, or else a form that can, at the discretion of the <A REL=DEFINITION HREF="26_glo_c.htm#code"><I>code</I></A> doing the expansion, be used in place of the original <A REL=DEFINITION HREF="26_glo_f.htm#form"><I>form</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_cmp_ma.htm#compiler-macro-function">compiler-macro-function</A> <A REL=DEFINITION HREF="m_define.htm#define-compiler-macro">define-compiler-macro</A>
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</PRE>
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<P><B>Figure 3-6. Defined names applicable to compiler macros</B> <P>
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<A REL=CHILD HREF="03_bbaa.htm"><H2>
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3.2.2.1.1 Purpose of Compiler Macros</H2></A><P>
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<A REL=CHILD HREF="03_bbab.htm"><H2>
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3.2.2.1.2 Naming of Compiler Macros</H2></A><P>
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<A REL=CHILD HREF="03_bbac.htm"><H2>
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3.2.2.1.3 When Compiler Macros Are Used</H2></A><P><HR>
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