78 lines
2.4 KiB
HTML
78 lines
2.4 KiB
HTML
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<!DOCTYPE HTML PUBLIC "-//W3O//DTD W3 HTML 2.0//EN">
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<!Originally converted to HTML using LaTeX2HTML 95 (Thu Jan 19 1995) by Nikos Drakos (nikos@cbl.leeds.ac.uk), CBLU, University of Leeds >
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<HEAD>
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<TITLE> let (SPECIAL FORM)</TITLE>
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</HEAD>
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<BODY>
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<meta name="description" value=" let (SPECIAL FORM)">
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<meta name="keywords" value="lp">
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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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<BR> <HR>
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<A HREF="node99.html"><IMG ALIGN=BOTTOM ALT="next" SRC="next_motif.gif"></A>
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<A HREF="node72.html"><IMG ALIGN=BOTTOM ALT="up" SRC="up_motif.gif"></A>
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<A HREF="node97.html"><IMG ALIGN=BOTTOM ALT="previous" SRC="previous_motif.gif"></A> <BR>
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<A HREF="lp.html"><B>Contents</B></A>
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<B> Next:</B>
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<A HREF="node99.html"> list (FUNCTION)</A>
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<B>Up:</B>
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<A HREF="node72.html"> Appendix: Selected Lisp </A>
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<B> Previous:</B>
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<A HREF="node97.html"> length (FUNCTION)</A>
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<BR> <HR> <P>
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<H1> let (SPECIAL FORM)</H1>
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<P>
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<b> Format:</b>
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<tt> (let ((<var1> <init1> )</tt>
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<tt> (<var2> <init2> )</tt>
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<tt> .</tt>
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<tt> .</tt>
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<tt> (<varN> <initN> ))</tt>
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<tt> <body> )</tt>
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<P>
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<b> Required arguments:</b>
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1
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<P>
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<tt> ((<var> <init> )...)</tt>: a list of zero or more lists having the
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form <tt> (<var> )</tt> or <tt> (<var> <init> )</tt>. <tt> <var> </tt> must be a
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symbol appropriate as the name of a variable. <tt> <init> </tt> may be
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any Lisp expression.
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<P>
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<b> Optional arguments:</b>
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arbitrary
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<P>
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<tt> <body> </tt>: any sequence of zero or more Lisp expressions.
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<P>
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The <tt> <var> </tt>'s are established as local variables for the
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expressions in <tt> <body> </tt>. If a <tt> <var> </tt> is not accompanied by an
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<tt><init> </tt> expression, it is initially bound to NIL. Otherwise, <tt> <init> </tt>
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is evaluated and assigned as the value of <tt> <var> </tt>. let evaluates
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all the expressions in <tt> <body> </tt> and returns the value of the last, or
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NIL if there are none.
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<P>
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<b> Examples:</b>
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<P>
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<BLOCKQUOTE>
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<PRE>> (let ((a)
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(b))
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(and (not a) (not b)))
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T
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> (let ((a 3)
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(b 4))
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(setf a (+ a b))
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(setf b (+ a b))
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(+ a b))
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18
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</PRE>
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</BLOCKQUOTE>
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<P>
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<BR> <HR>
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<P>
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<ADDRESS>
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<I>© Colin Allen & Maneesh Dhagat <BR>
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March 2007 </I>
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</ADDRESS>
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</BODY>
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