88 lines
5.1 KiB
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88 lines
5.1 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 LAST</TITLE>
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<A NAME="last"><I>Function</I> <B>LAST</B></A> <P>
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<P><B>Syntax:</B><P>
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<P>
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<B>last</B> <I>list <TT>&optional</TT> n</I> => <I>tail</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>list</I>---a <A REL=DEFINITION HREF="26_glo_l.htm#list"><I>list</I></A>, which might be a <A REL=DEFINITION HREF="26_glo_d.htm#dotted_list"><I>dotted list</I></A> but must not be a <A REL=DEFINITION HREF="26_glo_c.htm#circular_list"><I>circular list</I></A>. <P>
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<I>n</I>---a non-negative <A REL=DEFINITION HREF="26_glo_i.htm#integer"><I>integer</I></A>. The default is <TT>1</TT>. <P>
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<I>tail</I>---an <A REL=DEFINITION HREF="26_glo_o.htm#object"><I>object</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="#last"><B>last</B></A> returns the last <I>n</I> <A REL=DEFINITION HREF="26_glo_c.htm#cons"><I>conses</I></A> (not the last <I>n</I> elements) of <I>list</I>). If <I>list</I> is <TT>()</TT>, <A REL=DEFINITION HREF="#last"><B>last</B></A> returns <TT>()</TT>. <P>
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If <I>n</I> is zero, the atom that terminates <I>list</I> is returned. If <I>n</I> is greater than or equal to the number of <A REL=DEFINITION HREF="26_glo_c.htm#cons"><I>cons</I></A> cells in <I>list</I>, the result is <I>list</I>. <P>
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<P><B>Examples:</B><P>
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<P>
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<PRE>
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(last nil) => NIL
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(last '(1 2 3)) => (3)
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(last '(1 2 . 3)) => (2 . 3)
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(setq x (list 'a 'b 'c 'd)) => (A B C D)
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(last x) => (D)
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(rplacd (last x) (list 'e 'f)) x => (A B C D E F)
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(last x) => (F)
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(last '(a b c)) => (C)
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(last '(a b c) 0) => ()
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(last '(a b c) 1) => (C)
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(last '(a b c) 2) => (B C)
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(last '(a b c) 3) => (A B C)
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(last '(a b c) 4) => (A B C)
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(last '(a . b) 0) => B
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(last '(a . b) 1) => (A . B)
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(last '(a . b) 2) => (A . B)
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</PRE>
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</TT> <P>
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<P><B>Side Effects:</B> None.
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<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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The consequences are undefined if <I>list</I> is a <A REL=DEFINITION HREF="26_glo_c.htm#circular_list"><I>circular list</I></A>. Should 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>n</I> is not a non-negative <A REL=DEFINITION HREF="26_glo_i.htm#integer"><I>integer</I></A>. <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_butlas.htm#butlast"><B>butlast</B></A>, <A REL=DEFINITION HREF="f_nth.htm#nth"><B>nth</B></A> <P>
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<P><B>Notes:</B><P>
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<P>
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The following code could be used to define <A REL=DEFINITION HREF="#last"><B>last</B></A>. <P>
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<PRE>
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(defun last (list &optional (n 1))
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(check-type n (integer 0))
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(do ((l list (cdr l))
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(r list)
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(i 0 (+ i 1)))
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((atom l) r)
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(if (>= i n) (pop r))))
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</PRE>
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</TT> <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/iss209.htm">LAST-N</A><LI> <A REL=CHILD HREF="../Issues/iss138.htm">DOTTED-LIST-ARGUMENTS:CLARIFY</A><P></UL><HR>
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