125 lines
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125 lines
6.4 KiB
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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>7.3. Function Invocation</TITLE>
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</HEAD>
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<BODY>
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<meta name="description" value=" Function Invocation">
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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=tex2html2536 HREF="node82.html"><IMG ALIGN=BOTTOM ALT="next" SRC="icons/next_motif.gif"></A> <A NAME=tex2html2534 HREF="node76.html"><IMG ALIGN=BOTTOM ALT="up" SRC="icons/up_motif.gif"></A> <A NAME=tex2html2528 HREF="node80.html"><IMG ALIGN=BOTTOM ALT="previous" SRC="icons/previous_motif.gif"></A> <A NAME=tex2html2538 HREF="node1.html"><IMG ALIGN=BOTTOM ALT="contents" SRC="icons/contents_motif.gif"></A> <A NAME=tex2html2539 HREF="index.html"><IMG ALIGN=BOTTOM ALT="index" SRC="icons/index_motif.gif"></A> <BR>
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<B> Next:</B> <A NAME=tex2html2537 HREF="node82.html"> Simple Sequencing</A>
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<B>Up:</B> <A NAME=tex2html2535 HREF="node76.html"> Control Structure</A>
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<B> Previous:</B> <A NAME=tex2html2529 HREF="node80.html"> Generalized Variables</A>
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<HR> <P>
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<H1><A NAME=SECTION001130000000000000000>7.3. Function Invocation</A></H1>
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<P>
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The most primitive form for function invocation in Lisp of course
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has no name; any list that has no other interpretation
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as a macro call or special form is taken to be a function call.
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Other constructs are provided for less common but
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nevertheless frequently useful situations.
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<P>
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<BR><b>[Function]</b><BR>
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<tt>apply</tt> <tt><i>function arg</i></tt> <tt>&rest</tt> <tt><i>more-args</i></tt><P>This applies <i>function</i> to a list of arguments.<p>
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<img align=bottom alt="old_change_begin" src="gif/old_change_begin.gif"><br>
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The <i>function</i> may be a
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compiled-code object, or a lambda-expression, or a symbol; in the latter
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case the global functional value of that symbol is used (but it is
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illegal for the symbol to be the name of a macro or special form).
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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=6118> </A> to allow the <i>function</i>
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to be only of type <tt>symbol</tt> or <tt>function</tt>; a lambda-expression
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is no longer acceptable as a functional argument. One must use the
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<tt>function</tt> special form or the abbreviation <tt>#'</tt> before
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a lambda-expression that appears as an explicit argument 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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The arguments for the <i>function</i> consist of the last argument
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to <tt>apply</tt> appended to the end of a list of all the other
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arguments to <tt>apply</tt> but the <i>function</i> itself;
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it is as if all the arguments to <tt>apply</tt> except the <i>function</i>
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were given to <tt>list*</tt> to create the argument list.
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For example:
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<P><pre>
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(setq f '+) (apply f '(1 2)) => 3
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(setq f #'-) (apply f '(1 2)) => -1
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(apply #'max 3 5 '(2 7 3)) => 7
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(apply 'cons '((+ 2 3) 4)) =>
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((+ 2 3) . 4) <i>not</i> (5 . 4)
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(apply #'+ '()) => 0
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</pre><P>
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Note that if the function takes keyword arguments, the
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keywords as well as the corresponding values must appear in the argument
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list:
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<P><pre>
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(apply #'(lambda (<tt>&key</tt> a b) (list a b)) '(:b 3)) => (<tt>nil</tt> 3)
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</pre><P>
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This can be very useful in conjunction with the <tt>&allow-other-keys</tt> feature:
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<P><pre>
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(defun foo (size <tt>&rest</tt> keys <tt>&key</tt> double <tt>&allow-other-keys</tt>)
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(let ((v (apply #'make-array size :allow-other-keys t keys)))
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(if double (concatenate (type-of v) v v) v)))
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(foo 4 :initial-contents '(a b c d) :double t)
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=> #(a b c d a b c d)
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</pre><P>
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<P>
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<BR><b>[Function]</b><BR>
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<tt>funcall</tt> <tt><i>fn</i></tt> <tt>&rest</tt> <tt><i>arguments</i></tt><P><tt>(funcall <i>fn</i> <i>a1</i> <i>a2</i> ... <i>an</i>)</tt>
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applies the function <i>fn</i> to the arguments
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<i>a1</i>, <i>a2</i>, ..., <i>an</i>.
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The <i>fn</i> may not
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be a special form or a macro; this would not be meaningful.
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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=6158> </A> to allow the <i>fn</i>
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to be only of type <tt>symbol</tt> or <tt>function</tt>; a lambda-expression
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is no longer acceptable as a functional argument. One must use the
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<tt>function</tt> special form or the abbreviation <tt>#'</tt> before
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a lambda-expression that appears as an explicit argument 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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For example:
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<P><pre>
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(cons 1 2) => (1 . 2)
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(setq cons (symbol-function '+))
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(funcall cons 1 2) => 3
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</pre><P>
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The difference between <tt>funcall</tt> and an ordinary function call is that
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the function is obtained by ordinary Lisp evaluation rather than
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by the special interpretation of the function position that normally
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occurs.
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<P>
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<hr>
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<b>Compatibility note:</b> The Common Lisp function <tt>funcall</tt> corresponds roughly to
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the Interlisp primitive <tt>apply*</tt>.
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<hr>
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<P>
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<BR><b>[Constant]</b><BR>
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<tt>call-arguments-limit</tt><P>The value of <tt>call-arguments-limit</tt> is a positive integer that is
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the upper exclusive bound on the number of arguments that may
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be passed to a function. This bound depends on the implementation
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but will not be smaller than 50.
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(Implementors are encouraged to make this limit as large as practicable
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without sacrificing performance.)
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The value of <tt>call-arguments-limit</tt> must be at
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least as great as that of <tt>lambda-parameters-limit</tt>.
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See also <tt>multiple-values-limit</tt>.
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<P>
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<BR> <HR><A NAME=tex2html2536 HREF="node82.html"><IMG ALIGN=BOTTOM ALT="next" SRC="icons/next_motif.gif"></A> <A NAME=tex2html2534 HREF="node76.html"><IMG ALIGN=BOTTOM ALT="up" SRC="icons/up_motif.gif"></A> <A NAME=tex2html2528 HREF="node80.html"><IMG ALIGN=BOTTOM ALT="previous" SRC="icons/previous_motif.gif"></A> <A NAME=tex2html2538 HREF="node1.html"><IMG ALIGN=BOTTOM ALT="contents" SRC="icons/contents_motif.gif"></A> <A NAME=tex2html2539 HREF="index.html"><IMG ALIGN=BOTTOM ALT="index" SRC="icons/index_motif.gif"></A> <BR>
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<B> Next:</B> <A NAME=tex2html2537 HREF="node82.html"> Simple Sequencing</A>
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<B>Up:</B> <A NAME=tex2html2535 HREF="node76.html"> Control Structure</A>
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<B> Previous:</B> <A NAME=tex2html2529 HREF="node80.html"> Generalized Variables</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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