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<TITLE>Common LISP Hints: Funcall, Apply, and Mapcar</TITLE>
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<H2><A NAME="s20">20. Funcall, Apply, and Mapcar</A></H2>
<P>Earlier I promised to give some functions which take functions as
arguments. Here they are:</P>
<P>
<BLOCKQUOTE><CODE>
<PRE>
> (funcall #'+ 3 4)
7
> (apply #'+ 3 4 '(3 4))
14
> (mapcar #'not '(t nil t nil t nil))
(NIL T NIL T NIL T)
</PRE>
</CODE></BLOCKQUOTE>
</P>
<P><CODE>Funcall</CODE> calls its first argument on its remaining arguments.</P>
<P><CODE>Apply</CODE> is just like <CODE>funcall</CODE>, except that its final argument
should be a
list; the elements of that list are treated as if they were additional
arguments to a <CODE>funcall</CODE>.</P>
<P>The first argument to <CODE>mapcar</CODE> must be a function of one argument;
<CODE>mapcar</CODE>
applies this function to each element of a list and collects the
results in another list.</P>
<P><CODE>Funcall</CODE> and <CODE>apply</CODE> are chiefly useful when their first argument is a
variable. For instance, a search engine could take a heuristic function
as a parameter and use <CODE>funcall</CODE> or <CODE>apply</CODE> to call that function on a
state description. The sorting functions described later use <CODE>funcall</CODE>
to call their comparison functions.</P>
<P><CODE>Mapcar</CODE>, along with nameless functions (see below), can replace many
loops.</P>
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