55 lines
1.6 KiB
HTML
55 lines
1.6 KiB
HTML
<!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> null (PREDICATE)</TITLE>
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</HEAD>
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<BODY>
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<meta name="description" value=" null (PREDICATE)">
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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="node108.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="node106.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="node108.html"> numberp (PREDICATE)</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="node106.html"> nthcdr (FUNCTION)</A>
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<BR> <HR> <P>
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<H1> null (PREDICATE)</H1>
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<P>
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<b> Format:</b>
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<tt> (null <exp> )</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> <exp> </tt>: any Lisp expression
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<P>
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The predicate <tt>null</tt> returns T if <tt> <expr> </tt> evaluates to the empty list; NIL
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otherwise. <tt>null</tt> is just the same as <tt>not</tt>, but is the preferred form to use when
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the purpose is to test whether a list is empty.
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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>> (null '(picard riker))
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NIL
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> (null (rest '(picard)))
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T
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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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