72 lines
3.6 KiB
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72 lines
3.6 KiB
HTML
<!-- 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 6.1.6.1</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_af.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Previous]" SRC="../Graphics/Prev.gif" ALIGN=Bottom></A><A REL=UP HREF="06_af.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Up]" SRC="../Graphics/Up.gif" ALIGN=Bottom></A><A REL=NEXT HREF="06_ag.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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6.1.6.1 Examples of WHEN clause</H2> <P>
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<PRE>
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;; Signal an exceptional condition.
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(loop for item in '(1 2 3 a 4 5)
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when (not (numberp item))
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return (cerror "enter new value" "non-numeric value: ~s" item))
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Error: non-numeric value: A
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;; The previous example is equivalent to the following one.
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(loop for item in '(1 2 3 a 4 5)
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when (not (numberp item))
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do (return
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(cerror "Enter new value" "non-numeric value: ~s" item)))
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Error: non-numeric value: A
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</PRE>
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</TT> <P>
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<PRE>
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;; This example parses a simple printed string representation from
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;; BUFFER (which is itself a string) and returns the index of the
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;; closing double-quote character.
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(let ((buffer "\"a\" \"b\""))
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(loop initially (unless (char= (char buffer 0) #\")
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(loop-finish))
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for i of-type fixnum from 1 below (length (the string buffer))
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when (char= (char buffer i) #\")
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return i))
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=> 2
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;; The collected value is returned.
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(loop for i from 1 to 10
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when (> i 5)
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collect i
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finally (prin1 'got-here))
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>> GOT-HERE
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=> (6 7 8 9 10)
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;; Return both the count of collected numbers and the numbers.
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(loop for i from 1 to 10
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when (> i 5)
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collect i into number-list
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and count i into number-count
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finally (return (values number-count number-list)))
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=> 5, (6 7 8 9 10)
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</PRE>
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</TT> <P>
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