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226 lines
11 KiB
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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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<HTML>
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<HEAD>
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<TITLE>CLHS: Macro LOOP</TITLE>
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<META HTTP-EQUIV="Author" CONTENT="Kent M. Pitman">
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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="m_dolist.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Previous]" SRC="../Graphics/Prev.gif" ALIGN=Bottom></A><A REL=UP HREF="c_iterat.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Up]" SRC="../Graphics/Up.gif" ALIGN=Bottom></A><A REL=NEXT HREF="m_loop_f.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Next]" SRC="../Graphics/Next.gif" ALIGN=Bottom></A></H1>
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<HR>
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<A NAME="loop"><I>Macro</I> <B>LOOP</B></A> <P>
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<P>
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<P><B>Syntax:</B><P>
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<P>
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The ``simple'' <A REL=DEFINITION HREF="#loop"><B>loop</B></A> <A REL=DEFINITION HREF="26_glo_f.htm#form"><I>form</I></A>: <P>
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<B>loop</B> <I><I>compound-form</I><B>*</B></I> => <I><I>result</I><B>*</B></I><P>
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<P>
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The ``extended'' <A REL=DEFINITION HREF="#loop"><B>loop</B></A> <A REL=DEFINITION HREF="26_glo_f.htm#form"><I>form</I></A>: <P>
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<B>loop</B> <I>[<I>name-clause</I>] {<I>variable-clause</I>}<B>*</B> {<I>main-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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name-clause::= named name
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</PRE>
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<PRE>
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variable-clause::= with-clause | initial-final | for-as-clause
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</PRE>
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<PRE>
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with-clause::= with var1 [type-spec] [= form1] {and var2 [type-spec] [= form2]}*
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</PRE>
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<PRE>
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main-clause::= unconditional | accumulation | conditional | termination-test | initial-final
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</PRE>
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<PRE>
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initial-final::= initially compound-form+ | finally compound-form+
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</PRE>
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<PRE>
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unconditional::= {do | doing} compound-form+ | return {form | it}
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</PRE>
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<PRE>
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accumulation::= list-accumulation | numeric-accumulation
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</PRE>
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<PRE>
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list-accumulation::= {collect | collecting | append | appending | nconc | nconcing} {form | it}
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[into simple-var]
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</PRE>
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<PRE>
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numeric-accumulation::= {count | counting | sum | summing | }
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maximize | maximizing | minimize | minimizing {form | it}
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[into simple-var] [type-spec]
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</PRE>
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<PRE>
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conditional::= {if | when | unless} form selectable-clause {and selectable-clause}*
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[else selectable-clause {and selectable-clause}*]
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[end]
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</PRE>
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<PRE>
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selectable-clause::= unconditional | accumulation | conditional
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</PRE>
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<PRE>
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termination-test::= while form | until form | repeat form | always form | never form | thereis form
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</PRE>
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<PRE>
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for-as-clause::= {for | as} for-as-subclause {and for-as-subclause}*
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</PRE>
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<PRE>
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for-as-subclause::= for-as-arithmetic | for-as-in-list | for-as-on-list | for-as-equals-then |
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for-as-across | for-as-hash | for-as-package
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</PRE>
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<PRE>
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for-as-arithmetic::= var [type-spec] for-as-arithmetic-subclause
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</PRE>
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<PRE>
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for-as-arithmetic-subclause::= arithmetic-up | arithmetic-downto | arithmetic-downfrom
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</PRE>
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<PRE>
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arithmetic-up::= [[{from | upfrom} form1 | {to | upto | below} form2 | by form3]]+
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</PRE>
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<PRE>
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arithmetic-downto::= [[{{from form1}}1 | {{{downto | above} form2}}1 | by form3]]
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</PRE>
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<PRE>
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arithmetic-downfrom::= [[{{downfrom form1}}1 | {to | downto | above} form2 | by form3]]
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</PRE>
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<PRE>
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for-as-in-list::= var [type-spec] in form1 [by step-fun]
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</PRE>
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<PRE>
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for-as-on-list::= var [type-spec] on form1 [by step-fun]
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</PRE>
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<PRE>
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for-as-equals-then::= var [type-spec] = form1 [then form2]
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</PRE>
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<PRE>
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for-as-across::= var [type-spec] across vector
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</PRE>
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<PRE>
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for-as-hash::= var [type-spec] being {each | the}
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{{hash-key | hash-keys} {in | of} hash-table
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[using (hash-value other-var)] |
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{hash-value | hash-values} {in | of} hash-table
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[using (hash-key other-var)]}
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</PRE>
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<PRE>
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for-as-package::= var [type-spec] being {each | the}
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{symbol | symbols |
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present-symbol | present-symbols |
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external-symbol | external-symbols}
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[{in | of} package]
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</PRE>
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<PRE>
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type-spec::= simple-type-spec | destructured-type-spec
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</PRE>
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<PRE>
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simple-type-spec::= fixnum | float | t | nil
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</PRE>
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<PRE>
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destructured-type-spec::= of-type d-type-spec
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</PRE>
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<PRE>
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d-type-spec::= type-specifier | (d-type-spec . d-type-spec)
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</PRE>
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<PRE>
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var::= d-var-spec
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</PRE>
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<PRE>
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var1::= d-var-spec
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</PRE>
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<PRE>
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var2::= d-var-spec
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</PRE>
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<PRE>
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other-var::= d-var-spec
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</PRE>
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<PRE>
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d-var-spec::= simple-var | <A REL=DEFINITION HREF="a_nil.htm#nil">nil</A> | (d-var-spec . d-var-spec)
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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>compound-form</I>---a <A REL=DEFINITION HREF="26_glo_c.htm#compound_form"><I>compound form</I></A>. <P>
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<I>name</I>---a <A REL=DEFINITION HREF="26_glo_s.htm#symbol"><I>symbol</I></A>. <P>
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<I>simple-var</I>---a <A REL=DEFINITION HREF="26_glo_s.htm#symbol"><I>symbol</I></A> (a <A REL=DEFINITION HREF="26_glo_v.htm#variable"><I>variable</I></A> name). <P>
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<I>form</I>, <I>form1</I>, <I>form2</I>, <I>form3</I>---a <A REL=DEFINITION HREF="26_glo_f.htm#form"><I>form</I></A>. <P>
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<I>step-fun</I>---a <A REL=DEFINITION HREF="26_glo_f.htm#form"><I>form</I></A> that evaluates to a <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>function</I></A> of one <A REL=DEFINITION HREF="26_glo_a.htm#argument"><I>argument</I></A>. <P>
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<I>vector</I>---a <A REL=DEFINITION HREF="26_glo_f.htm#form"><I>form</I></A> that evaluates to a <A REL=DEFINITION HREF="26_glo_v.htm#vector"><I>vector</I></A>. <P>
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<I>hash-table</I>---a <A REL=DEFINITION HREF="26_glo_f.htm#form"><I>form</I></A> that evaluates to a <A REL=DEFINITION HREF="26_glo_h.htm#hash_table"><I>hash table</I></A>. <P>
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<I>package</I>---a <A REL=DEFINITION HREF="26_glo_f.htm#form"><I>form</I></A> that evaluates to a <A REL=DEFINITION HREF="26_glo_p.htm#package_designator"><I>package designator</I></A>. <P>
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<I>type-specifier</I>---a <A REL=DEFINITION HREF="26_glo_t.htm#type_specifier"><I>type specifier</I></A>. This might be either an <A REL=DEFINITION HREF="26_glo_a.htm#atomic_type_specifier"><I>atomic type specifier</I></A> or a <A REL=DEFINITION HREF="26_glo_c.htm#compound_type_specifier"><I>compound type specifier</I></A>, which introduces some additional complications to proper parsing in the face of destructuring; for further information, see <A REL=CHILD HREF="06_aag.htm">Section 6.1.1.7 (Destructuring)</A>. <P>
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<I>result</I>---an <A REL=DEFINITION HREF="26_glo_o.htm#object"><I>object</I></A>. <P>
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<P>
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<P><B>Description:</B><P>
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<P>
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For details, see <A REL=CHILD HREF="06_a.htm">Section 6.1 (The LOOP Facility)</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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;; An example of the simple form of LOOP.
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(defun sqrt-advisor ()
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(loop (format t "~&Number: ")
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(let ((n (parse-integer (read-line) :junk-allowed t)))
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(when (not n) (return))
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(format t "~&The square root of ~D is ~D.~%" n (sqrt n)))))
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=> SQRT-ADVISOR
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(sqrt-advisor)
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>> Number: 5<NEWLINE>
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>> The square root of 5 is 2.236068.
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>> Number: 4<NEWLINE>
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>> The square root of 4 is 2.
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>> Number: done<NEWLINE>
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=> NIL
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;; An example of the extended form of LOOP.
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(defun square-advisor ()
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(loop as n = (progn (format t "~&Number: ")
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(parse-integer (read-line) :junk-allowed t))
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while n
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do (format t "~&The square of ~D is ~D.~%" n (* n n))))
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=> SQUARE-ADVISOR
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(square-advisor)
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>> Number: 4<NEWLINE>
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>> The square of 4 is 16.
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>> Number: 23<NEWLINE>
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>> The square of 23 is 529.
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>> Number: done<NEWLINE>
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=> NIL
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;; Another example of the extended form of LOOP.
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(loop for n from 1 to 10
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when (oddp n)
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collect n)
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=> (1 3 5 7 9)
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</PRE>
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</TT> <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="m_do_do.htm#do"><B>do</B></A>, <A REL=DEFINITION HREF="m_dolist.htm#dolist"><B>dolist</B></A>, <A REL=DEFINITION HREF="m_dotime.htm#dotimes"><B>dotimes</B></A>, <A REL=DEFINITION HREF="m_return.htm#return"><B>return</B></A>, <A REL=DEFINITION HREF="s_go.htm#go"><B>go</B></A>, <A REL=DEFINITION HREF="s_throw.htm#throw"><B>throw</B></A>, <A REL=CHILD HREF="06_aag.htm">Section 6.1.1.7 (Destructuring)</A> <P>
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<P><B>Notes:</B><P>
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<P>
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Except that <A REL=DEFINITION HREF="m_loop_f.htm#loop-finish"><B>loop-finish</B></A> cannot be used within a simple <A REL=DEFINITION HREF="#loop"><B>loop</B></A> <A REL=DEFINITION HREF="26_glo_f.htm#form"><I>form</I></A>, a simple <A REL=DEFINITION HREF="#loop"><B>loop</B></A> <A REL=DEFINITION HREF="26_glo_f.htm#form"><I>form</I></A> is related to an extended <A REL=DEFINITION HREF="#loop"><B>loop</B></A> <A REL=DEFINITION HREF="26_glo_f.htm#form"><I>form</I></A> in the following way: <P>
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<PRE>
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(loop compound-form*) == (loop do compound-form*)
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</PRE>
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</TT> <P>
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<P><HR>The following <A REL=META HREF="../Front/X3J13Iss.htm">X3J13 cleanup issues</A>, <I>not part of the specification</I>, apply to this section:<P><UL><LI> <A REL=CHILD HREF="../Issues/iss223.htm">LOOP-MISCELLANEOUS-REPAIRS:FIX</A><LI> <A REL=CHILD HREF="../Issues/iss226.htm">LOOP-SYNTAX-OVERHAUL:REPAIR</A><P></UL><HR>
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<A REL=NAVIGATOR HREF="../Front/StartPts.htm"><IMG WIDTH=80 HEIGHT=40 ALT="[Starting Points]" SRC="../Graphics/StartPts.gif" ALIGN=Bottom></A><A REL=TOC HREF="../Front/Contents.htm"><IMG WIDTH=80 HEIGHT=40 ALT="[Contents]" SRC="../Graphics/Contents.gif" ALIGN=Bottom></A><A REL=INDEX HREF="../Front/X_Master.htm"><IMG WIDTH=80 HEIGHT=40 ALT="[Index]" SRC="../Graphics/Index.gif" ALIGN=Bottom></A><A REL=INDEX HREF="../Front/X_Symbol.htm"><IMG WIDTH=80 HEIGHT=40 ALT="[Symbols]" SRC="../Graphics/Symbols.gif" ALIGN=Bottom></A><A REL=GLOSSARY HREF="../Body/26_a.htm"><IMG WIDTH=80 HEIGHT=40 ALT="[Glossary]" SRC="../Graphics/Glossary.gif" ALIGN=Bottom></A><A HREF="../Front/X3J13Iss.htm"><IMG WIDTH=80 HEIGHT=40 ALT="[Issues]" SRC="../Graphics/Issues.gif" ALIGN=Bottom></A><BR>
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<A REL=COPYRIGHT HREF="../Front/Help.htm#Legal"><I>Copyright 1996-2005, LispWorks Ltd. All rights reserved.</I></A><P>
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</BODY>
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</HTML>
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