115 lines
2.6 KiB
HTML
115 lines
2.6 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> eql, equal (PREDICATES)</TITLE>
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</HEAD>
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<BODY>
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<meta name="description" value=" eql, equal (PREDICATES)">
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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="node93.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="node91.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="node93.html"> eval (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="node91.html"> documentation (FUNCTION)</A>
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<BR> <HR> <P>
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<H1> eql, equal (PREDICATES)</H1>
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<P>
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<b> Format:</b>
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<tt> (eql <exp1> <exp2> )</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> <exp1> </tt>: any Lisp expression
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<tt> <exp2> </tt>: any Lisp expression
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<P>
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Both argument expressions are evaluated. If they both return
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atoms, eql returns T if they are the same. If they return lists,
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eql returns T only if the lists are represented by the same object
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in memory. In contrast, two values can be ``equal'' if they are
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copies of one another (perhaps existing in different memory locations).
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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>> (eql 'hello 'hello)
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T
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> (eql -19 -19)
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T
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> (eql 2 3)
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NIL
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> (eql '(1 2 3) '(1 2 3))
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NIL
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> (setq a '(1 2 3))
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(1 2 3)
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> (setq b '(1 2 3))
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(1 2 3)
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> (eql a b)
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NIL
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> (setq c a)
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(1 2 3)
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> (eql a c)
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T
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> (eql b c)
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NIL
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</PRE>
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</BLOCKQUOTE>
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<P>
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<b> Format:</b>
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<tt> (equal <exp1> <exp2> )</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> <exp1> </tt>: any Lisp expression
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<tt> <exp2> </tt>: any Lisp expression
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<P>
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Both argument expressions are evaluated. If the values returned
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are copies of one another (or even are physically the same by
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occupying the same memory), equal returns T. In contrast, for two
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lists to be eql they must represent the same object in memory.
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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>> (equal 'hey 'hello)
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NIL
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> (equal -81 -81)
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T
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> (equal '(1 (2 3)) '(1 (2 3)))
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T
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> (setq a '(1 2 3))
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(1 2 3)
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> (setq b '(1 2 3))
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(1 2 3)
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> (equal a b)
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T
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> (setq c a)
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(1 2 3)
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> (equal a c)
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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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