73 lines
4.6 KiB
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73 lines
4.6 KiB
HTML
<!-- 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 INCF, DECF</TITLE>
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<A NAME="incf"><A NAME="decf"><I>Macro</I> <B>INCF, DECF</B></A></A> <P>
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<P><B>Syntax:</B><P>
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<P>
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<B>incf</B> <I>place [delta-form]</I> => <I>new-value</I><P>
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<B>decf</B> <I>place [delta-form]</I> => <I>new-value</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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<I>delta-form</I>---a <A REL=DEFINITION HREF="26_glo_f.htm#form"><I>form</I></A>; evaluated to produce a <I>delta</I>. The default is <TT>1</TT>. <P>
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<I>delta</I>---a <A REL=DEFINITION HREF="26_glo_n.htm#number"><I>number</I></A>. <P>
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<I>new-value</I>---a <A REL=DEFINITION HREF="26_glo_n.htm#number"><I>number</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="#incf"><B>incf</B></A> and <A REL=DEFINITION HREF="#decf"><B>decf</B></A> are used for incrementing and decrementing the <A REL=DEFINITION HREF="26_glo_v.htm#value"><I>value</I></A> of <I>place</I>, respectively. <P>
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The <I>delta</I> is added to (in the case of <A REL=DEFINITION HREF="#incf"><B>incf</B></A>) or subtracted from (in the case of <A REL=DEFINITION HREF="#decf"><B>decf</B></A>) the number in <I>place</I> and the result is stored in <I>place</I>. <P>
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Any necessary type conversions are performed automatically. <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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(setq n 0)
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(incf n) => 1
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n => 1
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(decf n 3) => -2
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n => -2
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(decf n -5) => 3
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(decf n) => 2
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(incf n 0.5) => 2.5
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(decf n) => 1.5
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n => 1.5
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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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<I>Place</I> is modified. <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="f_pl.htm#PL"><B>+</B></A>, <A REL=DEFINITION HREF="f__.htm#-"><B>-</B></A>, <A REL=DEFINITION HREF="f_1pl_1_.htm#1PL"><B>1+</B></A>, <A REL=DEFINITION HREF="f_1pl_1_.htm#1-"><B>1-</B></A>, <A REL=DEFINITION HREF="m_setf_.htm#setf"><B>setf</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/iss279.htm">PUSH-EVALUATION-ORDER:FIRST-ITEM</A><P></UL><HR>
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