94 lines
5.2 KiB
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94 lines
5.2 KiB
HTML
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<!-- Common Lisp HyperSpec (TM), version 7.0 generated by Kent M. Pitman on Mon, 11-Apr-2005 2:31am EDT -->
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<HTML>
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<HEAD>
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<TITLE>CLHS: Macro PSETQ</TITLE>
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<H1><A REV=MADE HREF="http://www.lispworks.com/"><IMG WIDTH=80 HEIGHT=65 ALT="[LISPWORKS]" SRC="../Graphics/LWSmall.gif" ALIGN=Bottom></A><A REL=TOP HREF="../Front/index.htm"><IMG WIDTH=237 HEIGHT=65 ALT="[Common Lisp HyperSpec (TM)]" SRC="../Graphics/CLHS_Sm.gif" ALIGN=Bottom></A> <A REL=PREV HREF="s_setq.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Previous]" SRC="../Graphics/Prev.gif" ALIGN=Bottom></A><A REL=UP HREF="c_data_a.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Up]" SRC="../Graphics/Up.gif" ALIGN=Bottom></A><A REL=NEXT HREF="s_block.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Next]" SRC="../Graphics/Next.gif" ALIGN=Bottom></A></H1>
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<HR>
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<A NAME="psetq"><I>Macro</I> <B>PSETQ</B></A> <P>
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<P><B>Syntax:</B><P>
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<P>
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<B>psetq</B> <I>{<I>pair</I>}<B>*</B></I> => <I><A REL=DEFINITION HREF="a_nil.htm#nil"><B>nil</B></A></I><P>
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<P>
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<PRE>
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pair::= var form
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</PRE>
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<P>
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<P><B>Pronunciation:</B><P>
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<P>
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<A REL=DEFINITION HREF="#psetq"><B>psetq</B></A>: [;pee'set,kyoo] <P>
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<P><B>Arguments and Values:</B><P>
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<P>
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<I>var</I>---a <A REL=DEFINITION HREF="26_glo_s.htm#symbol"><I>symbol</I></A> naming a <A REL=DEFINITION HREF="26_glo_v.htm#variable"><I>variable</I></A> other than a <A REL=DEFINITION HREF="26_glo_c.htm#constant_variable"><I>constant variable</I></A>. <P>
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<I>form</I>---a <A REL=DEFINITION HREF="26_glo_f.htm#form"><I>form</I></A>. <P>
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<P><B>Description:</B><P>
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<P>
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Assigns values to <A REL=DEFINITION HREF="26_glo_v.htm#variable"><I>variables</I></A>. <P>
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This is just like <A REL=DEFINITION HREF="s_setq.htm#setq"><B>setq</B></A>, except that the assignments happen ``in parallel.'' That is, first all of the forms are evaluated, and only then are the variables set to the resulting values. In this way, the assignment to one variable does not affect the value computation of another in the way that would occur with <A REL=DEFINITION HREF="s_setq.htm#setq"><B>setq</B></A>'s sequential assignment. <P>
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If any <I>var</I> refers to a <A REL=DEFINITION HREF="26_glo_b.htm#binding"><I>binding</I></A> made by <A REL=DEFINITION HREF="s_symbol.htm#symbol-macrolet"><B>symbol-macrolet</B></A>, then that <I>var</I> is treated as if <A REL=DEFINITION HREF="m_setf_.htm#psetf"><B>psetf</B></A> (not <A REL=DEFINITION HREF="#psetq"><B>psetq</B></A>) had been used. <P>
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<P><B>Examples:</B><P>
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<P>
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<PRE>
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;; A simple use of PSETQ to establish values for variables.
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;; As a matter of style, many programmers would prefer SETQ
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;; in a simple situation like this where parallel assignment
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;; is not needed, but the two have equivalent effect.
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(psetq a 1 b 2 c 3) => NIL
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a => 1
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b => 2
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c => 3
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;; Use of PSETQ to update values by parallel assignment.
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;; The effect here is very different than if SETQ had been used.
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(psetq a (1+ b) b (1+ a) c (+ a b)) => NIL
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a => 3
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b => 2
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c => 3
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;; Use of PSETQ on a symbol macro.
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(let ((x (list 10 20 30)))
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(symbol-macrolet ((y (car x)) (z (cadr x)))
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(psetq y (1+ z) z (1+ y))
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(list x y z)))
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=> ((21 11 30) 21 11)
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;; Use of parallel assignment to swap values of A and B.
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(let ((a 1) (b 2))
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(psetq a b b a)
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(values a b))
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=> 2, 1
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</PRE>
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</TT> <P>
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<P><B>Side Effects:</B><P>
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<P>
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The values of <I>forms</I> are assigned to <I>vars</I>. <P>
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<P><B>Affected By:</B> None.
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<P>
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<P><B>Exceptional Situations:</B> None.
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<P>
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<P><B>See Also:</B><P>
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<P>
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<A REL=DEFINITION HREF="m_setf_.htm#psetf"><B>psetf</B></A>, <A REL=DEFINITION HREF="s_setq.htm#setq"><B>setq</B></A> <P>
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<P><B>Notes:</B> None.
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<P>
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<P><HR>The following <A REL=META HREF="../Front/X3J13Iss.htm">X3J13 cleanup issue</A>, <I>not part of the specification</I>, applies to this section:<P><UL><LI> <A REL=CHILD HREF="../Issues/iss338.htm">SYMBOL-MACROLET-SEMANTICS:SPECIAL-FORM</A><P></UL><HR>
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<A REL=NAVIGATOR HREF="../Front/StartPts.htm"><IMG WIDTH=80 HEIGHT=40 ALT="[Starting Points]" SRC="../Graphics/StartPts.gif" ALIGN=Bottom></A><A REL=TOC HREF="../Front/Contents.htm"><IMG WIDTH=80 HEIGHT=40 ALT="[Contents]" SRC="../Graphics/Contents.gif" ALIGN=Bottom></A><A REL=INDEX HREF="../Front/X_Master.htm"><IMG WIDTH=80 HEIGHT=40 ALT="[Index]" SRC="../Graphics/Index.gif" ALIGN=Bottom></A><A REL=INDEX HREF="../Front/X_Symbol.htm"><IMG WIDTH=80 HEIGHT=40 ALT="[Symbols]" SRC="../Graphics/Symbols.gif" ALIGN=Bottom></A><A REL=GLOSSARY HREF="../Body/26_a.htm"><IMG WIDTH=80 HEIGHT=40 ALT="[Glossary]" SRC="../Graphics/Glossary.gif" ALIGN=Bottom></A><A HREF="../Front/X3J13Iss.htm"><IMG WIDTH=80 HEIGHT=40 ALT="[Issues]" SRC="../Graphics/Issues.gif" ALIGN=Bottom></A><BR>
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<A REL=COPYRIGHT HREF="../Front/Help.htm#Legal"><I>Copyright 1996-2005, LispWorks Ltd. All rights reserved.</I></A><P>
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