45 lines
1.8 KiB
HTML
45 lines
1.8 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> Using Your Own Definitions in New Functions</TITLE>
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</HEAD>
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<BODY>
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<meta name="description" value=" Using Your Own Definitions in New Functions">
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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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<BR> <HR>
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<A HREF="node20.html"><IMG ALIGN=BOTTOM ALT="next" SRC="next_motif.gif"></A>
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<A HREF="node15.html"><IMG ALIGN=BOTTOM ALT="up" SRC="up_motif.gif"></A>
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<A HREF="node18.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="node20.html"> Functions with Extended </A>
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<B>Up:</B>
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<A HREF="node15.html"> Defining Lisp functions</A>
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<B> Previous:</B>
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<A HREF="node18.html"> Using an Editor</A>
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<BR> <HR> <P>
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<H1> Using Your Own Definitions in New Functions</H1>
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<P>
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User-defined functions can be included in new function definitions. For example:
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<BLOCKQUOTE>
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<PRE>> (defun fourth-power (x)
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(square (square x)))
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FOURTH-POWER
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> (fourth-power 2)
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16
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</PRE>
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</BLOCKQUOTE>
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It is worth paying attention to what happens when fourth-power is called. During the computation, the variable ``x'' gets assigned as many as four times. First, x is bound to 2, which is its local value for the function fourth-power. Fourth-power evaluates (square (square 2)), which means that square is called once with the argument 2, and again with the argument 4. Each time square is called, a local version of x is bound to the appropriate value. Finally, x is restored to whatever global value it previously had.
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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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