86 lines
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86 lines
6.1 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: Macro SETF, PSETF</TITLE>
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<A NAME="setf"><A NAME="psetf"><I>Macro</I> <B>SETF, PSETF</B></A></A> <P>
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<P><B>Syntax:</B><P>
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<P>
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<B>setf</B> <I>{<I>pair</I>}<B>*</B></I> => <I><I>result</I><B>*</B></I><P>
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<B>psetf</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::= place newvalue
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</PRE>
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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>place</I>---a <A REL=DEFINITION HREF="26_glo_p.htm#place"><I>place</I></A>. <P>
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<I>newvalue</I>---a <A REL=DEFINITION HREF="26_glo_f.htm#form"><I>form</I></A>. <P>
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<I>results</I>---the <A REL=DEFINITION HREF="26_glo_m.htm#multiple_values"><I>multiple values</I></A>[2] returned by the storing form for the last <I>place</I>, or <A REL=DEFINITION HREF="a_nil.htm#nil"><B>nil</B></A> if there are no <I>pairs</I>. <P>
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<P><B>Description:</B><P>
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<P>
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<A REL=DEFINITION HREF="#setf"><B>setf</B></A> changes the <A REL=DEFINITION HREF="26_glo_v.htm#value"><I>value</I></A> of <I>place</I> to be <I>newvalue</I>. <P>
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<TT>(setf place newvalue)</TT> expands into an update form that stores the result of evaluating <I>newvalue</I> into the location referred to by <I>place</I>. Some <I>place</I> forms involve uses of accessors that take optional arguments. Whether those optional arguments are permitted by <A REL=DEFINITION HREF="#setf"><B>setf</B></A>, or what their use is, is up to the <A REL=DEFINITION HREF="#setf"><B>setf</B></A> expander function and is not under the control of <A REL=DEFINITION HREF="#setf"><B>setf</B></A>. The documentation for any <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>function</I></A> that accepts <TT>&optional</TT>, <TT>&rest</TT>, or <TT> ..... key</TT> arguments and that claims to be usable with <A REL=DEFINITION HREF="#setf"><B>setf</B></A> must specify how those arguments are treated. <P>
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If more than one <I>pair</I> is supplied, the <I>pairs</I> are processed sequentially; that is, <P>
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<PRE>
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(setf place-1 newvalue-1
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place-2 newvalue-2
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...
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place-N newvalue-N)
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</PRE>
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</TT> is precisely equivalent to <P>
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<PRE>
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(progn (setf place-1 newvalue-1)
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(setf place-2 newvalue-2)
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...
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(setf place-N newvalue-N))
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</PRE>
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</TT> For <A REL=DEFINITION HREF="#psetf"><B>psetf</B></A>, if more than one <I>pair</I> is supplied then the assignments of new values to places are done in parallel. More precisely, all <A REL=DEFINITION HREF="26_glo_s.htm#subform"><I>subforms</I></A> (in both the <I>place</I> and <I>newvalue</I> <A REL=DEFINITION HREF="26_glo_f.htm#form"><I>forms</I></A>) that are to be evaluated are evaluated from left to right; after all evaluations have been performed, all of the assignments are performed in an unpredictable order. <P>
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For detailed treatment of the expansion of <A REL=DEFINITION HREF="#setf"><B>setf</B></A> and <A REL=DEFINITION HREF="#psetf"><B>psetf</B></A>, see <A REL=CHILD HREF="05_ab.htm">Section 5.1.2 (Kinds of Places)</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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(setq x (cons 'a 'b) y (list 1 2 3)) => (1 2 3)
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(setf (car x) 'x (cadr y) (car x) (cdr x) y) => (1 X 3)
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x => (X 1 X 3)
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y => (1 X 3)
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(setq x (cons 'a 'b) y (list 1 2 3)) => (1 2 3)
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(psetf (car x) 'x (cadr y) (car x) (cdr x) y) => NIL
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x => (X 1 A 3)
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y => (1 A 3)
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</PRE>
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</TT> <P>
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<P><B>Affected By:</B><P>
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<P>
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<A REL=DEFINITION HREF="m_defi_3.htm#define-setf-expander"><B>define-setf-expander</B></A>, <A REL=DEFINITION HREF="m_defset.htm#defsetf"><B>defsetf</B></A>, <A REL=DEFINITION HREF="v_mexp_h.htm#STmacroexpand-hookST"><B>*macroexpand-hook*</B></A> <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_defi_3.htm#define-setf-expander"><B>define-setf-expander</B></A>, <A REL=DEFINITION HREF="m_defset.htm#defsetf"><B>defsetf</B></A>, <A REL=DEFINITION HREF="f_mexp_.htm#macroexpand-1"><B>macroexpand-1</B></A>, <A REL=DEFINITION HREF="m_rotate.htm#rotatef"><B>rotatef</B></A>, <A REL=DEFINITION HREF="m_shiftf.htm#shiftf"><B>shiftf</B></A>, <A REL=CHILD HREF="05_a.htm">Section 5.1 (Generalized Reference)</A> <P>
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<P><B>Notes:</B> None.
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<P>
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