74 lines
4.3 KiB
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74 lines
4.3 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: Accessor NTH</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_firstc.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_endp.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="nth"><I>Accessor</I> <B>NTH</B></A> <P>
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<P><B>Syntax:</B><P>
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<P>
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<B>nth</B> <I>n list</I> => <I>object</I><P>
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<TT>(setf (</TT><B>nth</B> <I>n list</I><TT>) </TT><I>new-object</I><TT>)</TT><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>n</I>---a non-negative <A REL=DEFINITION HREF="26_glo_i.htm#integer"><I>integer</I></A>. <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> or a <A REL=DEFINITION HREF="26_glo_c.htm#circular_list"><I>circular list</I></A>. <P>
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<I>object</I>---an <A REL=DEFINITION HREF="26_glo_o.htm#object"><I>object</I></A>. <P>
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<I>new-object</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="#nth"><B>nth</B></A> locates the <I>n</I>th element of <I>list</I>, where the <A REL=DEFINITION HREF="26_glo_c.htm#car"><I>car</I></A> of the <I>list</I> is the ``zeroth'' element. Specifically, <P>
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<PRE>
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(nth n list) == (car (nthcdr n list))
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</PRE>
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</TT> <P>
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<A REL=DEFINITION HREF="#nth"><B>nth</B></A> may be used to specify a <I>place</I> to <A REL=DEFINITION HREF="m_setf_.htm#setf"><B>setf</B></A>. Specifically, <P>
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<PRE>
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(setf (nth n list) new-object) == (setf (car (nthcdr n list)) new-object)
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</PRE>
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</TT> <P>
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<P><B>Examples:</B><P>
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<P>
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<PRE>
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(nth 0 '(foo bar baz)) => FOO
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(nth 1 '(foo bar baz)) => BAR
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(nth 3 '(foo bar baz)) => NIL
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(setq 0-to-3 (list 0 1 2 3)) => (0 1 2 3)
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(setf (nth 2 0-to-3) "two") => "two"
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0-to-3 => (0 1 "two" 3)
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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> 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_elt.htm#elt"><B>elt</B></A>, <A REL=DEFINITION HREF="f_firstc.htm#first"><B>first</B></A>, <A REL=DEFINITION HREF="f_nthcdr.htm#nthcdr"><B>nthcdr</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/iss138.htm">DOTTED-LIST-ARGUMENTS:CLARIFY</A><P></UL><HR>
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