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38 lines
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<TITLE>CLHS: Section 6.1.9</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_aha.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Previous]" SRC="../Graphics/Prev.gif" ALIGN=Bottom></A><A REL=UP HREF="06_a.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Up]" SRC="../Graphics/Up.gif" ALIGN=Bottom></A><A REL=NEXT HREF="c_iterat.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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6.1.9 Notes about Loop</H2> <P>
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<A REL=DEFINITION HREF="26_glo_t.htm#type"><I>Types</I></A> can be supplied for loop variables. It is not necessary to supply a <A REL=DEFINITION HREF="26_glo_t.htm#type"><I>type</I></A> for any variable, but supplying the <A REL=DEFINITION HREF="26_glo_t.htm#type"><I>type</I></A> can ensure that the variable has a correctly typed initial value, and it can also enable compiler optimizations (depending on the <A REL=DEFINITION HREF="26_glo_i.htm#implementation"><I>implementation</I></A>). <P>
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The clause <TT>repeat</TT> <I>n</I> ... is roughly equivalent to a clause such as <P>
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<PRE>
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(loop for internal-variable downfrom (- n 1) to 0 ...)
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</PRE>
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</TT> <P>
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but in some <A REL=DEFINITION HREF="26_glo_i.htm#implementation"><I>implementations</I></A>, the <TT>repeat</TT> construct might be more efficient. <P>
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Within the executable parts of the loop clauses and around the entire <A REL=DEFINITION HREF="m_loop.htm#loop"><B>loop</B></A> form, variables can be bound by using <A REL=DEFINITION HREF="s_let_l.htm#let"><B>let</B></A>. <P>
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Use caution when using a variable named <TT>IT</TT> (in any <A REL=DEFINITION HREF="26_glo_p.htm#package"><I>package</I></A>) in connection with <A REL=DEFINITION HREF="m_loop.htm#loop"><B>loop</B></A>, since <TT>it</TT> is a <A REL=DEFINITION HREF="26_glo_l.htm#loop_keyword"><I>loop keyword</I></A> that can be used in place of a <A REL=DEFINITION HREF="26_glo_f.htm#form"><I>form</I></A> in certain contexts. <P>
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There is no <A REL=DEFINITION HREF="26_glo_s.htm#standardized"><I>standardized</I></A> mechanism for users to add extensions to <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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