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31 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: Section 3.2.2.1.3.1</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_bbac.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Previous]" SRC="../Graphics/Prev.gif" ALIGN=Bottom></A><A REL=UP HREF="03_bbac.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Up]" SRC="../Graphics/Up.gif" ALIGN=Bottom></A><A REL=NEXT HREF="03_bbb.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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3.2.2.1.3.1 Notes about the Implementation of Compiler Macros</H2> <P>
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Although it is technically permissible, as described above, for <A REL=DEFINITION HREF="f_eval.htm#eval"><B>eval</B></A> to treat <A REL=DEFINITION HREF="26_glo_c.htm#compiler_macro"><I>compiler macros</I></A> in the same situations as <A REL=DEFINITION HREF="26_glo_c.htm#compiler"><I>compiler</I></A> might, this is not necessarily a good idea in <A REL=DEFINITION HREF="26_glo_i.htm#interpreted_implementation"><I>interpreted implementations</I></A>. <P>
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<A REL=DEFINITION HREF="26_glo_c.htm#compiler_macro"><I>Compiler macros</I></A> exist for the purpose of trading compile-time speed for run-time speed. Programmers who write <A REL=DEFINITION HREF="26_glo_c.htm#compiler_macro"><I>compiler macros</I></A> tend to assume that the <A REL=DEFINITION HREF="26_glo_c.htm#compiler_macro"><I>compiler macros</I></A> can take more time than normal <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>functions</I></A> and <A REL=DEFINITION HREF="26_glo_m.htm#macro"><I>macros</I></A> in order to produce code which is especially optimal for use at run time. Since <A REL=DEFINITION HREF="f_eval.htm#eval"><B>eval</B></A> in an <A REL=DEFINITION HREF="26_glo_i.htm#interpreted_implementation"><I>interpreted implementation</I></A> might perform semantic analysis of the same form multiple times, it might be inefficient in general for the <A REL=DEFINITION HREF="26_glo_i.htm#implementation"><I>implementation</I></A> to choose to call <A REL=DEFINITION HREF="26_glo_c.htm#compiler_macro"><I>compiler macros</I></A> on every such <A REL=DEFINITION HREF="26_glo_e.htm#evaluation"><I>evaluation</I></A>. <P>
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Nevertheless, the decision about what to do in these situations is left to each <A REL=DEFINITION HREF="26_glo_i.htm#implementation"><I>implementation</I></A>. <P>
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