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<TITLE>CLHS: Section 3.4.1.2</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="03_daa.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Previous]" SRC="../Graphics/Prev.gif" ALIGN=Bottom></A><A REL=UP HREF="03_da.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Up]" SRC="../Graphics/Up.gif" ALIGN=Bottom></A><A REL=NEXT HREF="03_dac.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Next]" SRC="../Graphics/Next.gif" ALIGN=Bottom></A></H1>
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<H2>
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3.4.1.2 Specifiers for optional parameters</H2> <P>
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If <TT>&optional</TT> is present, the optional parameter specifiers are those following <TT>&optional</TT> up to the next <A REL=DEFINITION HREF="26_glo_l.htm#lambda_list_keyword"><I>lambda list keyword</I></A> or the end of the list. If optional parameters are specified, then each one is processed as follows. If any unprocessed arguments remain, then the parameter variable <I>var</I> is bound to the next remaining argument, just as for a required parameter. If no arguments remain, however, then <I>init-form</I> is evaluated, and the parameter variable is bound to the resulting value (or to <A REL=DEFINITION HREF="a_nil.htm#nil"><B>nil</B></A> if no <I>init-form</I> appears in the parameter specifier). If another variable name <I>supplied-p-parameter</I> appears in the specifier, it is bound to <A REL=DEFINITION HREF="26_glo_t.htm#true"><I>true</I></A> if an argument had been available, and to <A REL=DEFINITION HREF="26_glo_f.htm#false"><I>false</I></A> if no argument remained (and therefore <I>init-form</I> had to be evaluated). <I>Supplied-p-parameter</I> is bound not to an argument but to a value indicating whether or not an argument had been supplied for the corresponding <I>var</I>. <P>
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