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91 lines
5.6 KiB
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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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<TITLE>CLHS: Accessor SYMBOL-VALUE</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="f_symb_4.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Previous]" SRC="../Graphics/Prev.gif" ALIGN=Bottom></A><A REL=UP HREF="c_symbol.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Up]" SRC="../Graphics/Up.gif" ALIGN=Bottom></A><A REL=NEXT HREF="f_get.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="symbol-value"><I>Accessor</I> <B>SYMBOL-VALUE</B></A> <P>
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<P><B>Syntax:</B><P>
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<P>
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<B>symbol-value</B> <I>symbol</I> => <I>value</I><P>
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<TT>(setf (</TT><B>symbol-value</B> <I>symbol</I><TT>) </TT><I>new-value</I><TT>)</TT><P>
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<P>
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<P><B>Arguments and Values:</B><P>
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<P>
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<I>symbol</I>---a <A REL=DEFINITION HREF="26_glo_s.htm#symbol"><I>symbol</I></A> that must have a <A REL=DEFINITION HREF="26_glo_v.htm#value"><I>value</I></A>. <P>
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<I>value</I>, <I>new-value</I>---an <A REL=DEFINITION HREF="26_glo_o.htm#object"><I>object</I></A>. <P>
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<P><B>Description:</B><P>
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<P>
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<A REL=DEFINITION HREF="26_glo_a.htm#access"><I>Accesses</I></A> the <A REL=DEFINITION HREF="26_glo_s.htm#symbol"><I>symbol</I></A>'s <A REL=DEFINITION HREF="26_glo_v.htm#value_cell"><I>value cell</I></A>. <P>
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<P><B>Examples:</B><P>
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<P>
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<PRE>
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(setf (symbol-value 'a) 1) => 1
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(symbol-value 'a) => 1
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;; SYMBOL-VALUE cannot see lexical variables.
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(let ((a 2)) (symbol-value 'a)) => 1
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(let ((a 2)) (setq a 3) (symbol-value 'a)) => 1
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;; SYMBOL-VALUE can see dynamic variables.
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(let ((a 2))
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(declare (special a))
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(symbol-value 'a)) => 2
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(let ((a 2))
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(declare (special a))
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(setq a 3)
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(symbol-value 'a)) => 3
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(let ((a 2))
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(setf (symbol-value 'a) 3)
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a) => 2
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a => 3
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(symbol-value 'a) => 3
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(let ((a 4))
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(declare (special a))
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(let ((b (symbol-value 'a)))
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(setf (symbol-value 'a) 5)
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(values a b))) => 5, 4
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a => 3
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(symbol-value :any-keyword) => :ANY-KEYWORD
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(symbol-value 'nil) => NIL
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(symbol-value '()) => NIL
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;; The precision of this next one is <A REL=DEFINITION HREF="26_glo_i.htm#implementation-dependent">implementation-dependent</A>.
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(symbol-value 'pi) => 3.141592653589793d0
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</PRE>
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</TT> <P>
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<P><B>Side Effects:</B> None.
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<P>
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<P><B>Affected By:</B><P>
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<P>
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<A REL=DEFINITION HREF="f_makunb.htm#makunbound"><B>makunbound</B></A>, <A REL=DEFINITION HREF="f_set.htm#set"><B>set</B></A>, <A REL=DEFINITION HREF="s_setq.htm#setq"><B>setq</B></A> <P>
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<P><B>Exceptional Situations:</B><P>
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<P>
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Should signal an error of <A REL=DEFINITION HREF="26_glo_t.htm#type"><I>type</I></A> <A REL=DEFINITION HREF="e_tp_err.htm#type-error"><B>type-error</B></A> if <I>symbol</I> is not a <A REL=DEFINITION HREF="26_glo_s.htm#symbol"><I>symbol</I></A>. <P>
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Should signal <A REL=DEFINITION HREF="e_unbo_1.htm#unbound-variable"><B>unbound-variable</B></A> if <I>symbol</I> is <A REL=DEFINITION HREF="26_glo_u.htm#unbound"><I>unbound</I></A> and an attempt is made to <A REL=DEFINITION HREF="26_glo_r.htm#read"><I>read</I></A> its <A REL=DEFINITION HREF="26_glo_v.htm#value"><I>value</I></A>. (No such error is signaled on an attempt to <A REL=DEFINITION HREF="26_glo_w.htm#write"><I>write</I></A> its <A REL=DEFINITION HREF="26_glo_v.htm#value"><I>value</I></A>.) <P>
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<P><B>See Also:</B><P>
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<P>
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<A REL=DEFINITION HREF="f_boundp.htm#boundp"><B>boundp</B></A>, <A REL=DEFINITION HREF="f_makunb.htm#makunbound"><B>makunbound</B></A>, <A REL=DEFINITION HREF="f_set.htm#set"><B>set</B></A>, <A REL=DEFINITION HREF="s_setq.htm#setq"><B>setq</B></A> <P>
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<P><B>Notes:</B><P>
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<P>
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<A REL=DEFINITION HREF="#symbol-value"><B>symbol-value</B></A> can be used to get the value of a <A REL=DEFINITION HREF="26_glo_c.htm#constant_variable"><I>constant variable</I></A>. <A REL=DEFINITION HREF="#symbol-value"><B>symbol-value</B></A> cannot <A REL=DEFINITION HREF="26_glo_a.htm#access"><I>access</I></A> the value of a <A REL=DEFINITION HREF="26_glo_l.htm#lexical_variable"><I>lexical variable</I></A>. <P>
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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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