81 lines
4.2 KiB
HTML
81 lines
4.2 KiB
HTML
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<!DOCTYPE HTML PUBLIC "-//W3O//DTD W3 HTML 2.0//EN">
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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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<HEAD>
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<TITLE>2.13. Functions</TITLE>
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</HEAD>
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<BODY>
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<meta name="description" value=" Functions">
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<meta name="keywords" value="clm">
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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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<b>Common Lisp the Language, 2nd Edition</b>
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<BR> <HR><A NAME=tex2html1999 HREF="node41.html"><IMG ALIGN=BOTTOM ALT="next" SRC="icons/next_motif.gif"></A> <A NAME=tex2html1997 HREF="node15.html"><IMG ALIGN=BOTTOM ALT="up" SRC="icons/up_motif.gif"></A> <A NAME=tex2html1991 HREF="node39.html"><IMG ALIGN=BOTTOM ALT="previous" SRC="icons/previous_motif.gif"></A> <A NAME=tex2html2001 HREF="node1.html"><IMG ALIGN=BOTTOM ALT="contents" SRC="icons/contents_motif.gif"></A> <A NAME=tex2html2002 HREF="index.html"><IMG ALIGN=BOTTOM ALT="index" SRC="icons/index_motif.gif"></A> <BR>
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<B> Next:</B> <A NAME=tex2html2000 HREF="node41.html"> Unreadable Data Objects</A>
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<B>Up:</B> <A NAME=tex2html1998 HREF="node15.html"> Data Types</A>
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<B> Previous:</B> <A NAME=tex2html1992 HREF="node39.html"> Structures</A>
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<HR> <P>
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<H1><A NAME=SECTION006130000000000000000>2.13. Functions</A></H1>
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<P>
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<img align=bottom alt="old_change_begin" src="gif/old_change_begin.gif"><br>
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<A NAME=FUNCTIONTYPESECTION>A</A>
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<i>function</i> is anything that may be correctly given to the <tt>funcall</tt>
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or <tt>apply</tt> function, and is
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to be executed as code when arguments are supplied.
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<P>
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A <i>compiled-function</i> is a compiled code object.
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<P>
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A lambda-expression
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(a list whose <i>car</i> is the symbol <tt>lambda</tt>) may serve as a function.
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Depending on the implementation, it may be possible for other lists to
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serve as functions. For example, an implementation might choose to
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represent a ``lexical closure'' as a list whose <i>car</i> contains some
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special marker.
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<P>
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A symbol may serve as a function; an attempt to invoke a symbol as a function
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causes the contents of the symbol's function cell to be used.
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See <tt>symbol-function</tt> and <tt>defun</tt>.
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<P>
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The result of evaluating a <tt>function</tt> special form
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will always be a function.
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<br><img align=bottom alt="old_change_end" src="gif/old_change_end.gif">
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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 June 1988 (FUNCTION-TYPE) <A NAME=1363> </A>
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to revise these specifications. The type <tt>function</tt> is to be disjoint
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from <tt>cons</tt> and <tt>symbol</tt>, and so a list whose <i>car</i> is <tt>lambda</tt>
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is not, properly speaking, of type <tt>function</tt>, nor is any symbol.
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However,
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standard Common Lisp functions that accept functional arguments
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will accept a symbol or a list whose <i>car</i> is <tt>lambda</tt>
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and automatically coerce it to be a function; such standard
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functions include <tt>funcall</tt>, <tt>apply</tt>, and <tt>mapcar</tt>.
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Such functions do not, however, accept a lambda-expression as a functional
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argument; therefore one may not write
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<P>
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<P><pre>
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(mapcar '(lambda (x y) (sqrt (* x y))) p q)
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</pre><P>
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but instead one must write something like
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<P><pre>
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(mapcar #'(lambda (x y) (sqrt (* x y))) p q)
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</pre><P>
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<P>
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This change makes it impermissible to represent a lexical closure
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as a list whose <i>car</i> is some special marker.
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<P>
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The value of a <tt>function</tt> special form
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will always be of type <tt>function</tt>.
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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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<BR> <HR><A NAME=tex2html1999 HREF="node41.html"><IMG ALIGN=BOTTOM ALT="next" SRC="icons/next_motif.gif"></A> <A NAME=tex2html1997 HREF="node15.html"><IMG ALIGN=BOTTOM ALT="up" SRC="icons/up_motif.gif"></A> <A NAME=tex2html1991 HREF="node39.html"><IMG ALIGN=BOTTOM ALT="previous" SRC="icons/previous_motif.gif"></A> <A NAME=tex2html2001 HREF="node1.html"><IMG ALIGN=BOTTOM ALT="contents" SRC="icons/contents_motif.gif"></A> <A NAME=tex2html2002 HREF="index.html"><IMG ALIGN=BOTTOM ALT="index" SRC="icons/index_motif.gif"></A> <BR>
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<B> Next:</B> <A NAME=tex2html2000 HREF="node41.html"> Unreadable Data Objects</A>
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<B>Up:</B> <A NAME=tex2html1998 HREF="node15.html"> Data Types</A>
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<B> Previous:</B> <A NAME=tex2html1992 HREF="node39.html"> Structures</A>
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<HR> <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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