86 lines
5.9 KiB
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86 lines
5.9 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 SIGNAL</TITLE>
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<A NAME="signal"><I>Function</I> <B>SIGNAL</B></A> <P>
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<P><B>Syntax:</B><P>
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<P>
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<B>signal</B> <I>datum <TT>&rest</TT> arguments</I> => <I><A REL=DEFINITION HREF="a_nil.htm#nil"><B>nil</B></A></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>datum</I>, <I>arguments</I>---<A REL=DEFINITION HREF="26_glo_d.htm#designator"><I>designators</I></A> for a <A REL=DEFINITION HREF="26_glo_c.htm#condition"><I>condition</I></A> of default type <A REL=DEFINITION HREF="e_smp_cn.htm#simple-condition"><B>simple-condition</B></A>. <P>
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<P><B>Description:</B><P>
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<P>
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<A REL=DEFINITION HREF="26_glo_s.htm#signal"><I>Signals</I></A> the <A REL=DEFINITION HREF="26_glo_c.htm#condition"><I>condition</I></A> denoted by the given <I>datum</I> and <I>arguments</I>. If the <A REL=DEFINITION HREF="26_glo_c.htm#condition"><I>condition</I></A> is not handled, <A REL=DEFINITION HREF="#signal"><B>signal</B></A> returns <A REL=DEFINITION HREF="a_nil.htm#nil"><B>nil</B></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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(defun handle-division-conditions (condition)
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(format t "Considering condition for division condition handling~%")
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(when (and (typep condition 'arithmetic-error)
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(eq '/ (arithmetic-error-operation condition)))
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(invoke-debugger condition)))
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HANDLE-DIVISION-CONDITIONS
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(defun handle-other-arithmetic-errors (condition)
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(format t "Considering condition for arithmetic condition handling~%")
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(when (typep condition 'arithmetic-error)
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(abort)))
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HANDLE-OTHER-ARITHMETIC-ERRORS
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(define-condition a-condition-with-no-handler (condition) ())
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A-CONDITION-WITH-NO-HANDLER
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(signal 'a-condition-with-no-handler)
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NIL
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(handler-bind ((condition #'handle-division-conditions)
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(condition #'handle-other-arithmetic-errors))
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(signal 'a-condition-with-no-handler))
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Considering condition for division condition handling
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Considering condition for arithmetic condition handling
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NIL
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(handler-bind ((arithmetic-error #'handle-division-conditions)
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(arithmetic-error #'handle-other-arithmetic-errors))
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(signal 'arithmetic-error :operation '* :operands '(1.2 b)))
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Considering condition for division condition handling
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Considering condition for arithmetic condition handling
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Back to Lisp Toplevel
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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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The debugger might be entered due to <A REL=DEFINITION HREF="v_break_.htm#STbreak-on-signalsST"><B>*break-on-signals*</B></A>. <P>
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Handlers for the condition being signaled might transfer control. <P>
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<P><B>Affected By:</B><P>
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<P>
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Existing handler bindings. <P>
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<A REL=DEFINITION HREF="v_break_.htm#STbreak-on-signalsST"><B>*break-on-signals*</B></A> <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="v_break_.htm#STbreak-on-signalsST"><B>*break-on-signals*</B></A>, <A REL=DEFINITION HREF="f_error.htm#error"><B>error</B></A>, <A REL=DEFINITION HREF="e_smp_cn.htm#simple-condition"><B>simple-condition</B></A>, <A REL=CHILD HREF="09_ad.htm">Section 9.1.4 (Signaling and Handling Conditions)</A> <P>
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<P><B>Notes:</B><P>
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<P>
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If <TT>(typep </TT><I>datum</I><TT> *break-on-signals*)</TT> <A REL=DEFINITION HREF="26_glo_y.htm#yield"><I>yields</I></A> <A REL=DEFINITION HREF="26_glo_t.htm#true"><I>true</I></A>, the debugger is entered prior to beginning the signaling process. The <A REL=DEFINITION HREF="a_contin.htm#continue"><B>continue</B></A> <A REL=DEFINITION HREF="26_glo_r.htm#restart"><I>restart</I></A> can be used to continue with the signaling process. This is also true for all other <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>functions</I></A> and <A REL=DEFINITION HREF="26_glo_m.htm#macro"><I>macros</I></A> that should, might, or must <A REL=DEFINITION HREF="26_glo_s.htm#signal"><I>signal</I></A> <A REL=DEFINITION HREF="26_glo_c.htm#condition"><I>conditions</I></A>. <P>
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