59 lines
5.4 KiB
HTML
59 lines
5.4 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 ENDP</TITLE>
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<A NAME="endp"><I>Function</I> <B>ENDP</B></A> <P>
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<P><B>Syntax:</B><P>
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<P>
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<B>endp</B> <I>list</I> => <I>generalized-boolean</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> or a <A REL=DEFINITION HREF="26_glo_c.htm#circular_list"><I>circular list</I></A>. <P>
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<I>generalized-boolean</I>---a <A REL=DEFINITION HREF="26_glo_g.htm#generalized_boolean"><I>generalized boolean</I></A>. <P>
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<P><B>Description:</B><P>
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<P>
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Returns <A REL=DEFINITION HREF="26_glo_t.htm#true"><I>true</I></A> if <I>list</I> is the <A REL=DEFINITION HREF="26_glo_e.htm#empty_list"><I>empty list</I></A>. Returns <A REL=DEFINITION HREF="26_glo_f.htm#false"><I>false</I></A> if <I>list</I> is a <A REL=DEFINITION HREF="26_glo_c.htm#cons"><I>cons</I></A>. <P>
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<P><B>Examples:</B><P>
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<P>
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<PRE>
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(endp nil) => <A REL=DEFINITION HREF="26_glo_t.htm#true">true</A>
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(endp '(1 2)) => <A REL=DEFINITION HREF="26_glo_f.htm#false">false</A>
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(endp (cddr '(1 2))) => <A REL=DEFINITION HREF="26_glo_t.htm#true">true</A>
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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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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>list</I> is not a <A REL=DEFINITION HREF="26_glo_l.htm#list"><I>list</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><P>
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<P>
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The purpose of <A REL=DEFINITION HREF="#endp"><B>endp</B></A> is to test for the end of <I>proper list</I>. Since <A REL=DEFINITION HREF="#endp"><B>endp</B></A> does not descend into a <A REL=DEFINITION HREF="26_glo_c.htm#cons"><I>cons</I></A>, it is well-defined to pass it a <A REL=DEFINITION HREF="26_glo_d.htm#dotted_list"><I>dotted list</I></A>. However, if shorter ``lists'' are iteratively produced by calling <A REL=DEFINITION HREF="f_car_c.htm#cdr"><B>cdr</B></A> on such a <A REL=DEFINITION HREF="26_glo_d.htm#dotted_list"><I>dotted list</I></A> and those ``lists'' are tested with <A REL=DEFINITION HREF="#endp"><B>endp</B></A>, a situation that has undefined consequences will eventually result when the <A REL=DEFINITION HREF="26_glo_n.htm#non-nil"><I>non-nil</I></A> <A REL=DEFINITION HREF="26_glo_a.htm#atom"><I>atom</I></A> (which is not in fact a <A REL=DEFINITION HREF="26_glo_l.htm#list"><I>list</I></A>) finally becomes the argument to <A REL=DEFINITION HREF="#endp"><B>endp</B></A>. Since this is the usual way in which <A REL=DEFINITION HREF="#endp"><B>endp</B></A> is used, it is conservative programming style and consistent with the intent of <A REL=DEFINITION HREF="#endp"><B>endp</B></A> to treat <A REL=DEFINITION HREF="#endp"><B>endp</B></A> as simply a function on <A REL=DEFINITION HREF="26_glo_p.htm#proper_list"><I>proper lists</I></A> which happens not to enforce an argument type of <A REL=DEFINITION HREF="26_glo_p.htm#proper_list"><I>proper list</I></A> except when the argument is <A REL=DEFINITION HREF="26_glo_a.htm#atomic"><I>atomic</I></A>. <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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