76 lines
5.3 KiB
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76 lines
5.3 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: Macro COND</TITLE>
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<A NAME="cond"><I>Macro</I> <B>COND</B></A> <P>
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<P><B>Syntax:</B><P>
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<P>
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<B>cond</B> <I>{<I>clause</I>}<B>*</B></I> => <I><I>result</I><B>*</B></I><P>
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<P>
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<PRE>
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clause::= (test-form form*)
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</PRE>
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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>test-form</I>---a <A REL=DEFINITION HREF="26_glo_f.htm#form"><I>form</I></A>. <P>
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<I>forms</I>---an <A REL=DEFINITION HREF="26_glo_i.htm#implicit_progn"><I>implicit progn</I></A>. <P>
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<I>results</I>---the <A REL=DEFINITION HREF="26_glo_v.htm#value"><I>values</I></A> of the <I>forms</I> in the first <I>clause</I> whose <I>test-form</I> <A REL=DEFINITION HREF="26_glo_y.htm#yield"><I>yields</I></A> <A REL=DEFINITION HREF="26_glo_t.htm#true"><I>true</I></A>, or the <A REL=DEFINITION HREF="26_glo_p.htm#primary_value"><I>primary value</I></A> of the <I>test-form</I> if there are no <I>forms</I> in that <I>clause</I>, or else <A REL=DEFINITION HREF="a_nil.htm#nil"><B>nil</B></A> if no <I>test-form</I> <A REL=DEFINITION HREF="26_glo_y.htm#yield"><I>yields</I></A> <A REL=DEFINITION HREF="26_glo_t.htm#true"><I>true</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="#cond"><B>cond</B></A> allows the execution of <I>forms</I> to be dependent on <I>test-form</I>. <P>
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<I>Test-forms</I> are evaluated one at a time in the order in which they are given in the argument list until a <I>test-form</I> is found that evaluates to <A REL=DEFINITION HREF="26_glo_t.htm#true"><I>true</I></A>. <P>
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If there are no <A REL=DEFINITION HREF="26_glo_f.htm#form"><I>forms</I></A> in that clause, the <A REL=DEFINITION HREF="26_glo_p.htm#primary_value"><I>primary value</I></A> of the <I>test-form</I> is returned by the <A REL=DEFINITION HREF="#cond"><B>cond</B></A> <A REL=DEFINITION HREF="26_glo_f.htm#form"><I>form</I></A>. Otherwise, the <I>forms</I> associated with this <I>test-form</I> are evaluated in order, left to right, as an <A REL=DEFINITION HREF="26_glo_i.htm#implicit_progn"><I>implicit progn</I></A>, and the <A REL=DEFINITION HREF="26_glo_v.htm#value"><I>values</I></A> returned by the last <I>form</I> are returned by the <A REL=DEFINITION HREF="#cond"><B>cond</B></A> <A REL=DEFINITION HREF="26_glo_f.htm#form"><I>form</I></A>. <P>
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Once one <I>test-form</I> has <I>yielded</I> <A REL=DEFINITION HREF="26_glo_t.htm#true"><I>true</I></A>, no additional <I>test-forms</I> are <I>evaluated</I>. If no <I>test-form</I> <A REL=DEFINITION HREF="26_glo_y.htm#yield"><I>yields</I></A> <A REL=DEFINITION HREF="26_glo_t.htm#true"><I>true</I></A>, <A REL=DEFINITION HREF="a_nil.htm#nil"><B>nil</B></A> is returned. <P>
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<P><B>Examples:</B><P>
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<P>
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<PRE>
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(defun select-options ()
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(cond ((= a 1) (setq a 2))
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((= a 2) (setq a 3))
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((and (= a 3) (floor a 2)))
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(t (floor a 3)))) => SELECT-OPTIONS
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(setq a 1) => 1
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(select-options) => 2
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a => 2
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(select-options) => 3
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a => 3
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(select-options) => 1
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(setq a 5) => 5
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(select-options) => 1, 2
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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="s_if.htm#if"><B>if</B></A>, <A REL=DEFINITION HREF="m_case_.htm#case"><B>case</B></A>. <P>
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<P><B>Notes:</B> None.
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<P>
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