85 lines
7.7 KiB
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85 lines
7.7 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 PUSHNEW</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_adjoin.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Previous]" SRC="../Graphics/Prev.gif" ALIGN=Bottom></A><A REL=UP HREF="c_conses.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Up]" SRC="../Graphics/Up.gif" ALIGN=Bottom></A><A REL=NEXT HREF="f_set_di.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="pushnew"><I>Macro</I> <B>PUSHNEW</B></A> <P>
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<P><B>Syntax:</B><P>
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<P>
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<B>pushnew</B> <I>item place <TT>&key</TT> key test test-not</I><P> => <I>new-place-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>item</I>---an <A REL=DEFINITION HREF="26_glo_o.htm#object"><I>object</I></A>. <P>
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<I>place</I>---a <A REL=DEFINITION HREF="26_glo_p.htm#place"><I>place</I></A>, the <A REL=DEFINITION HREF="26_glo_v.htm#value"><I>value</I></A> of which is a <A REL=DEFINITION HREF="26_glo_p.htm#proper_list"><I>proper list</I></A>. <P>
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<I>test</I>---a <A REL=DEFINITION HREF="26_glo_d.htm#designator"><I>designator</I></A> for a <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>function</I></A> of two <A REL=DEFINITION HREF="26_glo_a.htm#argument"><I>arguments</I></A> that returns a <A REL=DEFINITION HREF="26_glo_g.htm#generalized_boolean"><I>generalized boolean</I></A>. <P>
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<I>test-not</I>---a <A REL=DEFINITION HREF="26_glo_d.htm#designator"><I>designator</I></A> for a <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>function</I></A> of two <A REL=DEFINITION HREF="26_glo_a.htm#argument"><I>arguments</I></A> that returns a <A REL=DEFINITION HREF="26_glo_g.htm#generalized_boolean"><I>generalized boolean</I></A>. <P>
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<I>key</I>---a <A REL=DEFINITION HREF="26_glo_d.htm#designator"><I>designator</I></A> for a <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>function</I></A> of one argument, or <A REL=DEFINITION HREF="a_nil.htm#nil"><B>nil</B></A>. <P>
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<I>new-place-value</I>---a <A REL=DEFINITION HREF="26_glo_l.htm#list"><I>list</I></A> (the new <A REL=DEFINITION HREF="26_glo_v.htm#value"><I>value</I></A> of <I>place</I>). <P>
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<P><B>Description:</B><P>
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<P>
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<A REL=DEFINITION HREF="#pushnew"><B>pushnew</B></A> tests whether <I>item</I> is the same as any existing element of the <A REL=DEFINITION HREF="26_glo_l.htm#list"><I>list</I></A> stored in <I>place</I>. If <I>item</I> is not, it is prepended to the <A REL=DEFINITION HREF="26_glo_l.htm#list"><I>list</I></A>, and the new <A REL=DEFINITION HREF="26_glo_l.htm#list"><I>list</I></A> is stored in <I>place</I>. <P>
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<A REL=DEFINITION HREF="#pushnew"><B>pushnew</B></A> returns the new <A REL=DEFINITION HREF="26_glo_l.htm#list"><I>list</I></A> that is stored in <I>place</I>. <P>
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Whether or not <I>item</I> is already a member of the <A REL=DEFINITION HREF="26_glo_l.htm#list"><I>list</I></A> that is in <I>place</I> is determined by comparisons using <TT>:test</TT> or <TT>:test-not</TT>. The first argument to the <TT>:test</TT> or <TT>:test-not</TT> function is <I>item</I>; the second argument is an element of the <A REL=DEFINITION HREF="26_glo_l.htm#list"><I>list</I></A> in <I>place</I> as returned by the <TT>:key</TT> function (if supplied). <P>
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If <TT>:key</TT> is supplied, it is used to extract the part to be tested from both <I>item</I> and the <A REL=DEFINITION HREF="26_glo_l.htm#list"><I>list</I></A> element, as for <A REL=DEFINITION HREF="f_adjoin.htm#adjoin"><B>adjoin</B></A>. <P>
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The argument to the <TT>:key</TT> function is an element of the <A REL=DEFINITION HREF="26_glo_l.htm#list"><I>list</I></A> stored in <I>place</I>. The <TT>:key</TT> function typically returns part part of the element of the <A REL=DEFINITION HREF="26_glo_l.htm#list"><I>list</I></A>. If <TT>:key</TT> is not supplied or <A REL=DEFINITION HREF="a_nil.htm#nil"><B>nil</B></A>, the <A REL=DEFINITION HREF="26_glo_l.htm#list"><I>list</I></A> element is used. <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>place</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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It is <A REL=DEFINITION HREF="26_glo_i.htm#implementation-dependent"><I>implementation-dependent</I></A> whether or not <A REL=DEFINITION HREF="#pushnew"><B>pushnew</B></A> actually executes the storing form for its <I>place</I> in the situation where the <I>item</I> is already a member of the <A REL=DEFINITION HREF="26_glo_l.htm#list"><I>list</I></A> held by <I>place</I>. <P>
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<P><B>Examples:</B><P>
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<PRE>
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(setq x '(a (b c) d)) => (A (B C) D)
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(pushnew 5 (cadr x)) => (5 B C)
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x => (A (5 B C) D)
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(pushnew 'b (cadr x)) => (5 B C)
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x => (A (5 B C) D)
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(setq lst '((1) (1 2) (1 2 3))) => ((1) (1 2) (1 2 3))
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(pushnew '(2) lst) => ((2) (1) (1 2) (1 2 3))
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(pushnew '(1) lst) => ((1) (2) (1) (1 2) (1 2 3))
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(pushnew '(1) lst :test 'equal) => ((1) (2) (1) (1 2) (1 2 3))
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(pushnew '(1) lst :key #'car) => ((1) (2) (1) (1 2) (1 2 3))
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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 contents of <I>place</I> may be 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="m_push.htm#push"><B>push</B></A>, <A REL=DEFINITION HREF="f_adjoin.htm#adjoin"><B>adjoin</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
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<PRE>
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(pushnew item place :test p)
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</PRE>
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</TT> is roughly equivalent to
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<PRE>
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(setf place (adjoin item place :test p))
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</PRE>
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</TT> except that the <A REL=DEFINITION HREF="26_glo_s.htm#subform"><I>subforms</I></A> of <TT>place</TT> are evaluated only once, and <TT>item</TT> is evaluated before <TT>place</TT>. <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/iss281.htm">PUSHNEW-STORE-REQUIRED:UNSPECIFIED</A><LI> <A REL=CHILD HREF="../Issues/iss279.htm">PUSH-EVALUATION-ORDER:FIRST-ITEM</A><P></UL><HR>
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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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