41 lines
2.2 KiB
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41 lines
2.2 KiB
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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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<TITLE>5.1.1. Self-Evaluating Forms</TITLE>
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<meta name="description" value=" Self-Evaluating Forms">
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<meta name="resource-type" value="document">
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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=tex2html2227 HREF="node58.html"><IMG ALIGN=BOTTOM ALT="next" SRC="icons/next_motif.gif"></A> <A NAME=tex2html2225 HREF="node56.html"><IMG ALIGN=BOTTOM ALT="up" SRC="icons/up_motif.gif"></A> <A NAME=tex2html2219 HREF="node56.html"><IMG ALIGN=BOTTOM ALT="previous" SRC="icons/previous_motif.gif"></A> <A NAME=tex2html2229 HREF="node1.html"><IMG ALIGN=BOTTOM ALT="contents" SRC="icons/contents_motif.gif"></A> <A NAME=tex2html2230 HREF="index.html"><IMG ALIGN=BOTTOM ALT="index" SRC="icons/index_motif.gif"></A> <BR>
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<B> Next:</B> <A NAME=tex2html2228 HREF="node58.html"> Variables</A>
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<B>Up:</B> <A NAME=tex2html2226 HREF="node56.html"> Forms</A>
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<B> Previous:</B> <A NAME=tex2html2220 HREF="node56.html"> Forms</A>
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<HR> <P>
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<H2><A NAME=SECTION00911000000000000000>5.1.1. Self-Evaluating Forms</A></H2>
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<P>
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All numbers, characters, strings, and bit-vectors
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are <i>self-evaluating</i> forms.
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When such an object is evaluated, that object
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(or possibly a copy in the case of numbers or characters)
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is returned as the value
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of the form. The empty list <tt>()</tt>, which is also the false value <tt>nil</tt>,
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is also a self-evaluating form: the value of <tt>nil</tt> is <tt>nil</tt>.
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Keywords (symbols written with a leading colon) also evaluate
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to themselves: the value of <tt>:start</tt> is <tt>:start</tt>.
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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 January 1989 (CONSTANT-MODIFICATION) <A NAME=2982> </A> to clarify that
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it is an error to destructively modify any object that appears as a constant
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in executable code, whether as
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a self-evaluating form or within a <tt>quote</tt> special form.
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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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