72 lines
7.2 KiB
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72 lines
7.2 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: Function REVERSE, NREVERSE</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_length.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Previous]" SRC="../Graphics/Prev.gif" ALIGN=Bottom></A><A REL=UP HREF="c_sequen.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Up]" SRC="../Graphics/Up.gif" ALIGN=Bottom></A><A REL=NEXT HREF="f_sort_.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="reverse"><A NAME="nreverse"><I>Function</I> <B>REVERSE, NREVERSE</B></A></A> <P>
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<P><B>Syntax:</B><P>
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<P>
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<B>reverse</B> <I>sequence</I> => <I>reversed-sequence</I><P>
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<P>
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<B>nreverse</B> <I>sequence</I> => <I>reversed-sequence</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>sequence</I>---a <A REL=DEFINITION HREF="26_glo_p.htm#proper_sequence"><I>proper sequence</I></A>. <P>
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<I>reversed-sequence</I>---a <A REL=DEFINITION HREF="26_glo_s.htm#sequence"><I>sequence</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="#reverse"><B>reverse</B></A> and <A REL=DEFINITION HREF="#nreverse"><B>nreverse</B></A> return a new <A REL=DEFINITION HREF="26_glo_s.htm#sequence"><I>sequence</I></A> of the same kind as <I>sequence</I>, containing the same <A REL=DEFINITION HREF="26_glo_e.htm#element"><I>elements</I></A>, but in reverse order. <P>
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<A REL=DEFINITION HREF="#reverse"><B>reverse</B></A> and <A REL=DEFINITION HREF="#nreverse"><B>nreverse</B></A> differ in that <A REL=DEFINITION HREF="#reverse"><B>reverse</B></A> always creates and returns a new <A REL=DEFINITION HREF="26_glo_s.htm#sequence"><I>sequence</I></A>, whereas <A REL=DEFINITION HREF="#nreverse"><B>nreverse</B></A> might modify and return the given <I>sequence</I>. <A REL=DEFINITION HREF="#reverse"><B>reverse</B></A> never modifies the given <I>sequence</I>. <P>
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For <A REL=DEFINITION HREF="#reverse"><B>reverse</B></A>, if <I>sequence</I> is a <A REL=DEFINITION HREF="26_glo_v.htm#vector"><I>vector</I></A>, the result is a <A REL=DEFINITION HREF="26_glo_f.htm#fresh"><I>fresh</I></A> <A REL=DEFINITION HREF="26_glo_s.htm#simple_array"><I>simple array</I></A> of <A REL=DEFINITION HREF="26_glo_r.htm#rank"><I>rank</I></A> one that has the same <A REL=DEFINITION HREF="26_glo_a.htm#actual_array_element_type"><I>actual array element type</I></A> as <I>sequence</I>. If <I>sequence</I> is a <A REL=DEFINITION HREF="26_glo_l.htm#list"><I>list</I></A>, the result is a <A REL=DEFINITION HREF="26_glo_f.htm#fresh"><I>fresh</I></A> <A REL=DEFINITION HREF="26_glo_l.htm#list"><I>list</I></A>. <P>
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For <A REL=DEFINITION HREF="#nreverse"><B>nreverse</B></A>, if <I>sequence</I> is a <A REL=DEFINITION HREF="26_glo_v.htm#vector"><I>vector</I></A>, the result is a <A REL=DEFINITION HREF="26_glo_v.htm#vector"><I>vector</I></A> that has the same <A REL=DEFINITION HREF="26_glo_a.htm#actual_array_element_type"><I>actual array element type</I></A> as <I>sequence</I>. If <I>sequence</I> is a <A REL=DEFINITION HREF="26_glo_l.htm#list"><I>list</I></A>, the result is a <A REL=DEFINITION HREF="26_glo_l.htm#list"><I>list</I></A>. <P>
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For <A REL=DEFINITION HREF="#nreverse"><B>nreverse</B></A>, <I>sequence</I> might be destroyed and re-used to produce the result. The result might or might not be <A REL=DEFINITION HREF="26_glo_i.htm#identical"><I>identical</I></A> to <I>sequence</I>. Specifically, when <I>sequence</I> is a <A REL=DEFINITION HREF="26_glo_l.htm#list"><I>list</I></A>, <A REL=DEFINITION HREF="#nreverse"><B>nreverse</B></A> is permitted to <A REL=DEFINITION HREF="m_setf_.htm#setf"><B>setf</B></A> any part, <A REL=DEFINITION HREF="f_car_c.htm#car"><B>car</B></A> or <A REL=DEFINITION HREF="f_car_c.htm#cdr"><B>cdr</B></A>, of any <A REL=DEFINITION HREF="26_glo_c.htm#cons"><I>cons</I></A> that is part of the <A REL=DEFINITION HREF="26_glo_l.htm#list_structure"><I>list structure</I></A> of <I>sequence</I>. When <I>sequence</I> is a <A REL=DEFINITION HREF="26_glo_v.htm#vector"><I>vector</I></A>, <A REL=DEFINITION HREF="#nreverse"><B>nreverse</B></A> is permitted to re-order the elements of <I>sequence</I> in order to produce the resulting <A REL=DEFINITION HREF="26_glo_v.htm#vector"><I>vector</I></A>. <P>
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<P><B>Examples:</B><P>
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<PRE>
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(setq str "abc") => "abc"
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(reverse str) => "cba"
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str => "abc"
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(setq str (copy-seq str)) => "abc"
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(nreverse str) => "cba"
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str => <A REL=DEFINITION HREF="26_glo_i.htm#implementation-dependent">implementation-dependent</A>
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(setq l (list 1 2 3)) => (1 2 3)
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(nreverse l) => (3 2 1)
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l => <A REL=DEFINITION HREF="26_glo_i.htm#implementation-dependent">implementation-dependent</A>
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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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<A REL=DEFINITION HREF="#nreverse"><B>nreverse</B></A> might either create a new <A REL=DEFINITION HREF="26_glo_s.htm#sequence"><I>sequence</I></A>, modify the argument <I>sequence</I>, or both. (<A REL=DEFINITION HREF="#reverse"><B>reverse</B></A> does not modify <I>sequence</I>.) <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><P>
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<P>
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Should be prepared to 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>sequence</I> is not a <A REL=DEFINITION HREF="26_glo_p.htm#proper_sequence"><I>proper sequence</I></A>. <P>
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<P><B>See Also:</B> None.
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<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/iss293.htm">REMF-DESTRUCTION-UNSPECIFIED:X3J13-MAR-89</A><P></UL><HR>
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