67 lines
1.9 KiB
HTML
67 lines
1.9 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> if (SPECIAL FORM)</TITLE>
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</HEAD>
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<BODY>
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<meta name="description" value=" if (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="node97.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="node95.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="node97.html"> length (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="node95.html"> first (FUNCTION)</A>
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<BR> <HR> <P>
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<H1> if (SPECIAL FORM)</H1>
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<P>
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<b> Format:</b>
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<tt> (if <test> </tt>
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<tt> <then> </tt>
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<tt> <else> )</tt>
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<P>
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<b> Required arguments:</b>
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2
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<P>
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<tt> <test> </tt>: any Lisp expression
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<tt> <then> </tt>: any Lisp expression
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<P>
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<b> Optional arguments:</b>
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1
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<P>
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<tt> <else> </tt>: any Lisp expression
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<P>
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The <tt> <test> </tt> expression is evaluated; if it returns a value other than NIL, if returns the result of evaluating the <tt> <then> </tt> expression. If <tt> <test> </tt> evaluates to NIL, and no <tt> <else> </tt> expression is provided, NIL is returned. Otherwise the result of evaluating <tt> <else> </tt>is returned.
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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>> (if (> 4 3) 4 3)
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4
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> (if (< 4 3)
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(- 4 3)
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(- 3 4))
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-1
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> (if (= 4 3) t)
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NIL
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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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