93 lines
6.8 KiB
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93 lines
6.8 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: Function COMPUTE-RESTARTS</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="t_rst.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Previous]" SRC="../Graphics/Prev.gif" ALIGN=Bottom></A><A REL=UP HREF="c_condit.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Up]" SRC="../Graphics/Up.gif" ALIGN=Bottom></A><A REL=NEXT HREF="f_find_r.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Next]" SRC="../Graphics/Next.gif" ALIGN=Bottom></A></H1>
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<A NAME="compute-restarts"><I>Function</I> <B>COMPUTE-RESTARTS</B></A> <P>
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<P><B>Syntax:</B><P>
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<P>
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<B>compute-restarts</B> <I><TT>&optional</TT> condition</I> => <I>restarts</I><P>
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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>condition</I>---a <A REL=DEFINITION HREF="26_glo_c.htm#condition"><I>condition</I></A> <A REL=DEFINITION HREF="26_glo_o.htm#object"><I>object</I></A>, or <A REL=DEFINITION HREF="a_nil.htm#nil"><B>nil</B></A>. <P>
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<I>restarts</I>---a <A REL=DEFINITION HREF="26_glo_l.htm#list"><I>list</I></A> of <A REL=DEFINITION HREF="26_glo_r.htm#restart"><I>restarts</I></A>. <P>
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<P><B>Description:</B><P>
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<P>
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<A REL=DEFINITION HREF="#compute-restarts"><B>compute-restarts</B></A> uses the dynamic state of the program to compute a <A REL=DEFINITION HREF="26_glo_l.htm#list"><I>list</I></A> of the <A REL=DEFINITION HREF="26_glo_r.htm#restart"><I>restarts</I></A> which are currently active. <P>
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The resulting <A REL=DEFINITION HREF="26_glo_l.htm#list"><I>list</I></A> is ordered so that the innermost (more-recently established) restarts are nearer the head of the <A REL=DEFINITION HREF="26_glo_l.htm#list"><I>list</I></A>. <P>
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When <I>condition</I> is <A REL=DEFINITION HREF="26_glo_n.htm#non-nil"><I>non-nil</I></A>, only those <A REL=DEFINITION HREF="26_glo_r.htm#restart"><I>restarts</I></A> are considered that are either explicitly associated with that <I>condition</I>, or not associated with any <A REL=DEFINITION HREF="26_glo_c.htm#condition"><I>condition</I></A>; that is, the excluded <A REL=DEFINITION HREF="26_glo_r.htm#restart"><I>restarts</I></A> are those that are associated with a non-empty set of <A REL=DEFINITION HREF="26_glo_c.htm#condition"><I>conditions</I></A> of which the given <I>condition</I> is not an <A REL=DEFINITION HREF="26_glo_e.htm#element"><I>element</I></A>. If <I>condition</I> is <A REL=DEFINITION HREF="a_nil.htm#nil"><B>nil</B></A>, all <A REL=DEFINITION HREF="26_glo_r.htm#restart"><I>restarts</I></A> are considered. <P>
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<A REL=DEFINITION HREF="#compute-restarts"><B>compute-restarts</B></A> returns all <A REL=DEFINITION HREF="26_glo_a.htm#applicable_restart"><I>applicable restarts</I></A>, including anonymous ones, even if some of them have the same name as others and would therefore not be found by <A REL=DEFINITION HREF="f_find_r.htm#find-restart"><B>find-restart</B></A> when given a <A REL=DEFINITION HREF="26_glo_s.htm#symbol"><I>symbol</I></A> argument. <P>
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Implementations are permitted, but not required, to return <A REL=DEFINITION HREF="26_glo_d.htm#distinct"><I>distinct</I></A> <A REL=DEFINITION HREF="26_glo_l.htm#list"><I>lists</I></A> from repeated calls to <A REL=DEFINITION HREF="#compute-restarts"><B>compute-restarts</B></A> while in the same dynamic environment. The consequences are undefined if the <A REL=DEFINITION HREF="26_glo_l.htm#list"><I>list</I></A> returned by <A REL=DEFINITION HREF="#compute-restarts"><B>compute-restarts</B></A> is every modified. <P>
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<P><B>Examples:</B><P>
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<P>
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<PRE>
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;; One possible way in which an interactive debugger might present
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;; restarts to the user.
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(defun invoke-a-restart ()
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(let ((restarts (compute-restarts)))
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(do ((i 0 (+ i 1)) (r restarts (cdr r))) ((null r))
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(format t "~&~D: ~A~%" i (car r)))
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(let ((n nil) (k (length restarts)))
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(loop (when (and (typep n 'integer) (>= n 0) (< n k))
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(return t))
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(format t "~&Option: ")
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(setq n (read))
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(fresh-line))
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(invoke-restart-interactively (nth n restarts)))))
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(restart-case (invoke-a-restart)
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(one () 1)
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(two () 2)
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(nil () :report "Who knows?" 'anonymous)
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(one () 'I)
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(two () 'II))
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>> 0: ONE
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>> 1: TWO
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>> 2: Who knows?
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>> 3: ONE
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>> 4: TWO
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>> 5: Return to Lisp Toplevel.
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>> Option: 4
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=> II
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;; Note that in addition to user-defined restart points, COMPUTE-RESTARTS
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;; also returns information about any system-supplied restarts, such as
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;; the "Return to Lisp Toplevel" restart offered above.
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</PRE>
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</TT> <P>
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<P><B>Side Effects:</B> None.
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<P>
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<P><B>Affected By:</B><P>
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<P>
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Existing restarts. <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="f_find_r.htm#find-restart"><B>find-restart</B></A>, <A REL=DEFINITION HREF="f_invo_1.htm#invoke-restart"><B>invoke-restart</B></A>, <A REL=DEFINITION HREF="m_rst_bi.htm#restart-bind"><B>restart-bind</B></A> <P>
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<P><B>Notes:</B> None.
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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/iss076.htm">CONDITION-RESTARTS:PERMIT-ASSOCIATION</A><P></UL><HR>
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