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2.7 KiB
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51 lines
2.7 KiB
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<!DOCTYPE HTML PUBLIC "-//W3O//DTD W3 HTML 2.0//EN">
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<!Converted with LaTeX2HTML 0.6.5 (Tue Nov 15 1994) by Nikos Drakos (nikos@cbl.leeds.ac.uk), CBLU, University of Leeds >
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<HEAD>
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<TITLE>8.3. Destructuring</TITLE>
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</HEAD>
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<BODY>
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<meta name="description" value=" Destructuring">
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<meta name="keywords" value="clm">
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<meta name="resource-type" value="document">
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<meta name="distribution" value="global">
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<P>
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<b>Common Lisp the Language, 2nd Edition</b>
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<BR> <HR><A NAME=tex2html2770 HREF="node101.html"><IMG ALIGN=BOTTOM ALT="next" SRC="icons/next_motif.gif"></A> <A NAME=tex2html2768 HREF="node97.html"><IMG ALIGN=BOTTOM ALT="up" SRC="icons/up_motif.gif"></A> <A NAME=tex2html2762 HREF="node99.html"><IMG ALIGN=BOTTOM ALT="previous" SRC="icons/previous_motif.gif"></A> <A NAME=tex2html2772 HREF="node1.html"><IMG ALIGN=BOTTOM ALT="contents" SRC="icons/contents_motif.gif"></A> <A NAME=tex2html2773 HREF="index.html"><IMG ALIGN=BOTTOM ALT="index" SRC="icons/index_motif.gif"></A> <BR>
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<B> Next:</B> <A NAME=tex2html2771 HREF="node101.html"> Compiler Macros</A>
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<B>Up:</B> <A NAME=tex2html2769 HREF="node97.html"> Macros</A>
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<B> Previous:</B> <A NAME=tex2html2763 HREF="node99.html"> Macro Expansion</A>
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<HR> <P>
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<H1><A NAME=SECTION001230000000000000000>8.3. Destructuring</A></H1>
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<P>
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<img align=bottom alt="change_begin" src="gif/change_begin.gif"><br>
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X3J13 voted in March 1989 (DESTRUCTURING-BIND) <A NAME=8600> </A>
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to make the destructuring feature of <tt>defmacro</tt>
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available as a separate facility.
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<P>
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<BR><b>[Macro]</b><BR>
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<pre>
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destructuring-bind <i>lambda-list</i> <i>expression</i> {<i>declaration</i>}* {<i>form</i>}*
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</pre>
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<P> This macro binds the variables specified in <i>lambda-list</i> to the corresponding
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values in the tree structure resulting from evaluating the <i>expression</i>,
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then executes the <i>form</i>s as an implicit <tt>progn</tt>.
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<P>
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A <tt>destructuring-bind</tt> <i>lambda-list</i> may contain
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the lambda-list keywords <tt>&optional</tt>, <tt>&rest</tt>, <tt>&key</tt>,
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<tt>&allow-other-keys</tt>, and <tt>&aux</tt>; <tt>&body</tt> and <tt>&whole</tt>
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may also be used as they are in <tt>defmacro</tt>, but <tt>&environment</tt> may
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<i>not</i> be used. Nested and dotted lambda-lists are also permitted
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as for <tt>defmacro</tt>.
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The idea is that a <tt>destructuring-bind</tt> <i>lambda-list</i>
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has the same format as inner levels of a <tt>defmacro</tt> lambda-list.
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<P>
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If the result of evaluating the <i>expression</i> does not match the
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destructuring pattern, an error should be signaled.
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<br><img align=bottom alt="change_end" src="gif/change_end.gif">
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<P>
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<HR>
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<P><ADDRESS>
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AI.Repository@cs.cmu.edu
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</ADDRESS>
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</BODY>
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