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42 lines
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<!-- 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: Section 6.1.1.3</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="06_aab.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Previous]" SRC="../Graphics/Prev.gif" ALIGN=Bottom></A><A REL=UP HREF="06_aa.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Up]" SRC="../Graphics/Up.gif" ALIGN=Bottom></A><A REL=NEXT HREF="06_aad.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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6.1.1.3 Parsing Loop Clauses</H2> <P>
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The syntactic parts of an extended <A REL=DEFINITION HREF="m_loop.htm#loop"><B>loop</B></A> <A REL=DEFINITION HREF="26_glo_f.htm#form"><I>form</I></A> are called clauses; the rules for parsing are determined by that clause's keyword. The following example shows a <A REL=DEFINITION HREF="m_loop.htm#loop"><B>loop</B></A> <A REL=DEFINITION HREF="26_glo_f.htm#form"><I>form</I></A> with six clauses: <P>
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<PRE>
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(loop for i from 1 to (compute-top-value) ; first clause
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while (not (unacceptable i)) ; second clause
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collect (square i) ; third clause
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do (format t "Working on ~D now" i) ; fourth clause
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when (evenp i) ; fifth clause
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do (format t "~D is a non-odd number" i)
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finally (format t "About to exit!")) ; sixth clause
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</PRE>
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</TT> <P>
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Each <A REL=DEFINITION HREF="26_glo_l.htm#loop_keyword"><I>loop keyword</I></A> introduces either a compound loop clause or a simple loop clause that can consist of a <A REL=DEFINITION HREF="26_glo_l.htm#loop_keyword"><I>loop keyword</I></A> followed by a single <A REL=DEFINITION HREF="26_glo_f.htm#form"><I>form</I></A>. The number of <A REL=DEFINITION HREF="26_glo_f.htm#form"><I>forms</I></A> in a clause is determined by the <A REL=DEFINITION HREF="26_glo_l.htm#loop_keyword"><I>loop keyword</I></A> that begins the clause and by the auxiliary keywords in the clause. The keywords <TT>do</TT>, <TT>doing</TT>, <TT>initially</TT>, and <TT>finally</TT> are the only loop keywords that can take any number of <A REL=DEFINITION HREF="26_glo_f.htm#form"><I>forms</I></A> and group them as an <A REL=DEFINITION HREF="26_glo_i.htm#implicit_progn"><I>implicit progn</I></A>. <P>
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Loop clauses can contain auxiliary keywords, which are sometimes called prepositions. For example, the first clause in the code above includes the prepositions <TT>from</TT> and <TT>to</TT>, which mark the value from which stepping begins and the value at which stepping ends. <P>
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For detailed information about <A REL=DEFINITION HREF="m_loop.htm#loop"><B>loop</B></A> syntax, see the <A REL=DEFINITION HREF="26_glo_m.htm#macro"><I>macro</I></A> <A REL=DEFINITION HREF="m_loop.htm#loop"><B>loop</B></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/iss223.htm">LOOP-MISCELLANEOUS-REPAIRS:FIX</A><P></UL><HR>
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