97 lines
3 KiB
HTML
97 lines
3 KiB
HTML
<!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> setf (MACRO)</TITLE>
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</HEAD>
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<BODY>
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<meta name="description" value=" setf (MACRO)">
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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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<P>
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<BR> <HR>
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<A HREF="node114.html"><IMG ALIGN=BOTTOM ALT="next" SRC="next_motif.gif"></A>
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<A HREF="node112.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="node114.html"> symbolp (PREDICATE)</A>
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<B>Up:</B>
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<A HREF="node72.html"> Appendix: Selected Lisp </A>
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<B> Previous:</B>
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<A HREF="node112.html"> secondthird, etc. </A>
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<BR> <HR> <P>
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<H1> setf (MACRO)</H1>
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<P>
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<b> Format:</b>
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<BLOCKQUOTE>
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<PRE>(setf <place1> <val1>
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<place2> <val2>
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.
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.
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<placeN> <valN> )
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</PRE>
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</BLOCKQUOTE>
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<P>
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<b> Required arguments:</b> none
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<P>
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<b> Optional arguments:</b> any even number of arguments
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<P>
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<tt> <place> </tt>: either (i) the name of a variable, or (ii) an expression referring to part of a larger structure (e.g. a list, property list, structure, or array).
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<tt> <val> </tt>: any Lisp expression.
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<P>
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setf assigns the result of evaluating <tt> <val> </tt> to the location
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specified in the immediately preceding <tt> <place> </tt>. It returns the
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result of evaluating the last <tt> <val> </tt>. If no <tt> <place> -<val> </tt>
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pairs are specified, setf returns nil. setf is used, among other
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things, to assign values to variables, change parts of list structures,
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and to manage property lists and structures. Examples of all these uses
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are given in the chapters of this book. Other uses, too numerous to document
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here, can be found in Steele.
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<P>
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<b> Examples:</b> (see all chapters for further examples)
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<P>
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<BLOCKQUOTE>
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<PRE>> (setf crew '(picard riker worf crusher))
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(PICARD RIKER WORF CRUSHER)
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> (setf (first crew) (list 'captain (first crew))
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(second crew) (list 'commander (second crew))
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(third crew) (list 'lieutenant (third crew))
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(fourth crew) (list 'ensign (fourth crew)))
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(ENSIGN CRUSHER)
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> crew
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((CAPTAIN PICARD) (COMMANDER RIKER) (LIEUTENANT WORF)
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(ENSIGN CRUSHER))
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> (setf (get 'picard 'rank) 'captain)
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CAPTAIN
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> (get 'picard 'rank)
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CAPTAIN
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> (defstruct starship crew captain)
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STARSHIP
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> (setf enterprise (make-starship))
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#S(STARSHIP CREW NIL CAPTAIN NIL)
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> (setf (starship-crew enterprise) (rest crew)
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(starship-captain enterprise) (second (first crew)))
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PICARD
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> enterprise
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#S(STARSHIP CREW
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((COMMANDER RIKER) (LIEUTENANT WORF) (ENSIGN CRUSHER))
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CAPTAIN PICARD)
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</PRE>
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</BLOCKQUOTE>
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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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