93 lines
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93 lines
6.1 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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<TITLE>CLHS: Local Macro LOOP-FINISH</TITLE>
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<A NAME="loop-finish"><I>Local Macro</I> <B>LOOP-FINISH</B></A> <P>
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<P><B>Syntax:</B><P>
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<P>
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<B>loop-finish</B> <I><I><no arguments></I></I> =>| <P>
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<P>
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<P><B>Description:</B><P>
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<P>
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The <A REL=DEFINITION HREF="#loop-finish"><B>loop-finish</B></A> <A REL=DEFINITION HREF="26_glo_m.htm#macro"><I>macro</I></A> can be used lexically within 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> to terminate that <A REL=DEFINITION HREF="26_glo_f.htm#form"><I>form</I></A> ``normally.'' That is, it transfers control to the loop epilogue of the lexically innermost 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>. This permits execution of any <B>finally</B> clause (for effect) and the return of any accumulated result. <P>
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<P><B>Examples:</B><P>
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<P>
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<PRE>
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;; Terminate the loop, but return the accumulated count.
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(loop for i in '(1 2 3 stop-here 4 5 6)
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when (symbolp i) do (loop-finish)
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count i)
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=> 3
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;; The preceding loop is equivalent to:
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(loop for i in '(1 2 3 stop-here 4 5 6)
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until (symbolp i)
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count i)
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=> 3
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;; While LOOP-FINISH can be used can be used in a variety of
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;; situations it is really most needed in a situation where a need
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;; to exit is detected at other than the loop's `top level'
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;; (where UNTIL or WHEN often work just as well), or where some
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;; computation must occur between the point where a need to exit is
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;; detected and the point where the exit actually occurs. For example:
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(defun tokenize-sentence (string)
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(macrolet ((add-word (wvar svar)
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`(when ,wvar
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(push (coerce (nreverse ,wvar) 'string) ,svar)
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(setq ,wvar nil))))
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(loop with word = '() and sentence = '() and endpos = nil
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for i below (length string)
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do (let ((char (aref string i)))
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(case char
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(#\Space (add-word word sentence))
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(#\. (setq endpos (1+ i)) (loop-finish))
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(otherwise (push char word))))
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finally (add-word word sentence)
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(return (values (nreverse sentence) endpos)))))
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=> TOKENIZE-SENTENCE
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(tokenize-sentence "this is a sentence. this is another sentence.")
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=> ("this" "is" "a" "sentence"), 19
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(tokenize-sentence "this is a sentence")
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=> ("this" "is" "a" "sentence"), NIL
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</PRE>
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</TT> <P>
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<P><B>Side Effects:</B><P>
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<P>
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Transfers control. <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><P>
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<P>
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Whether or not <A REL=DEFINITION HREF="#loop-finish"><B>loop-finish</B></A> is <A REL=DEFINITION HREF="26_glo_f.htm#fbound"><I>fbound</I></A> in the <A REL=DEFINITION HREF="26_glo_g.htm#global_environment"><I>global environment</I></A> is <A REL=DEFINITION HREF="26_glo_i.htm#implementation-dependent"><I>implementation-dependent</I></A>; however, the restrictions on redefinition and <I>shadowing</I> of <A REL=DEFINITION HREF="#loop-finish"><B>loop-finish</B></A> are the same as for <A REL=DEFINITION HREF="26_glo_s.htm#symbol"><I>symbols</I></A> in the <TT>COMMON-LISP</TT> package which are <A REL=DEFINITION HREF="26_glo_f.htm#fbound"><I>fbound</I></A> in the <A REL=DEFINITION HREF="26_glo_g.htm#global_environment"><I>global environment</I></A>. The consequences of attempting to use <A REL=DEFINITION HREF="#loop-finish"><B>loop-finish</B></A> outside of <A REL=DEFINITION HREF="m_loop.htm#loop"><B>loop</B></A> are undefined. <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_loop.htm#loop"><B>loop</B></A>, <A REL=CHILD HREF="06_a.htm">Section 6.1 (The LOOP Facility)</A> <P>
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<P><B>Notes:</B><P>
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<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/iss211.htm">LEXICAL-CONSTRUCT-GLOBAL-DEFINITION:UNDEFINED</A><P></UL><HR>
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