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70 lines
5.2 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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<HTML>
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<HEAD>
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<TITLE>CLHS: Macro ROTATEF</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="m_shiftf.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="e_contro.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="rotatef"><I>Macro</I> <B>ROTATEF</B></A> <P>
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<P><B>Syntax:</B><P>
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<P>
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<B>rotatef</B> <I><I>place</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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<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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<P><B>Description:</B><P>
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<P>
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<A REL=DEFINITION HREF="#rotatef"><B>rotatef</B></A> modifies the values of each <I>place</I> by rotating values from one <I>place</I> into another. <P>
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If a <I>place</I> produces more values than there are store variables, the extra values are ignored. If a <I>place</I> produces fewer values than there are store variables, the missing values are set to <A REL=DEFINITION HREF="a_nil.htm#nil"><B>nil</B></A>. <P>
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In the form <TT>(rotatef </TT><I>place1</I><TT> </TT><I>place2</I><TT> ... </TT><I>placen</I><TT>)</TT>, the values in <I>place1</I> through <I>placen</I> are <A REL=DEFINITION HREF="26_glo_r.htm#read"><I>read</I></A> and <I>written</I>. Values 2 through <I>n</I> and value 1 are then stored into <I>place1</I> through <I>placen</I>. It is as if all the places form an end-around shift register that is rotated one place to the left, with the value of <I>place1</I> being shifted around the end to <I>placen</I>. <P>
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For information about the <A REL=DEFINITION HREF="26_glo_e.htm#evaluation"><I>evaluation</I></A> of <A REL=DEFINITION HREF="26_glo_s.htm#subform"><I>subforms</I></A> of <I>places</I>, see <A REL=CHILD HREF="05_aaa.htm">Section 5.1.1.1 (Evaluation of Subforms to Places)</A>. <P>
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<P><B>Examples:</B><P>
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<PRE>
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(let ((n 0)
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(x (list 'a 'b 'c 'd 'e 'f 'g)))
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(rotatef (nth (incf n) x)
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(nth (incf n) x)
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(nth (incf n) x))
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x) => (A C D B E F G)
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</PRE>
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</TT> <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_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="m_setf_.htm#setf"><B>setf</B></A>, <A REL=DEFINITION HREF="m_shiftf.htm#shiftf"><B>shiftf</B></A>, <A REL=DEFINITION HREF="v_mexp_h.htm#STmacroexpand-hookST"><B>*macroexpand-hook*</B></A>, <A REL=CHILD HREF="05_a.htm">Section 5.1 (Generalized Reference)</A> <P>
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<P><B>Notes:</B><P>
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<P>
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The effect of <TT>(rotatef </TT><I>place1</I><TT> </TT><I>place2</I><TT> ... </TT><I>placen</I><TT>)</TT> is roughly equivalent to <P>
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<PRE>
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(psetf place1 place2
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place2 place3
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...
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placen place1)
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</PRE>
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</TT> except that the latter would evaluate any <A REL=DEFINITION HREF="26_glo_s.htm#subform"><I>subforms</I></A> of each <TT>place</TT> twice, whereas <A REL=DEFINITION HREF="#rotatef"><B>rotatef</B></A> evaluates them once. <P>
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<P><HR>The following <A REL=META HREF="../Front/X3J13Iss.htm">X3J13 cleanup issues</A>, <I>not part of the specification</I>, apply to this section:<P><UL><LI> <A REL=CHILD HREF="../Issues/iss279.htm">PUSH-EVALUATION-ORDER:FIRST-ITEM</A><LI> <A REL=CHILD HREF="../Issues/iss309.htm">SETF-MULTIPLE-STORE-VARIABLES:ALLOW</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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