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81 lines
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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: Macro TRACE, UNTRACE</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="f_desc_1.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Previous]" SRC="../Graphics/Prev.gif" ALIGN=Bottom></A><A REL=UP HREF="c_enviro.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Up]" SRC="../Graphics/Up.gif" ALIGN=Bottom></A><A REL=NEXT HREF="m_step.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Next]" SRC="../Graphics/Next.gif" ALIGN=Bottom></A></H1>
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<A NAME="trace"><A NAME="untrace"><I>Macro</I> <B>TRACE, UNTRACE</B></A></A> <P>
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<P><B>Syntax:</B><P>
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<P>
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<B>trace</B> <I><I>function-name</I><B>*</B></I> => <I>trace-result</I><P>
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<B>untrace</B> <I><I>function-name</I><B>*</B></I> => <I>untrace-result</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>function-name</I>---a <A REL=DEFINITION HREF="26_glo_f.htm#function_name"><I>function name</I></A>. <P>
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<I>trace-result</I>---<A REL=DEFINITION HREF="26_glo_i.htm#implementation-dependent"><I>implementation-dependent</I></A>, unless no <I>function-names</I> are supplied, in which case <I>trace-result</I> is a <A REL=DEFINITION HREF="26_glo_l.htm#list"><I>list</I></A> of <A REL=DEFINITION HREF="26_glo_f.htm#function_name"><I>function names</I></A>. <P>
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<I>untrace-result</I>---<A REL=DEFINITION HREF="26_glo_i.htm#implementation-dependent"><I>implementation-dependent</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="#trace"><B>trace</B></A> and <A REL=DEFINITION HREF="#untrace"><B>untrace</B></A> control the invocation of the trace facility. <P>
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Invoking <A REL=DEFINITION HREF="#trace"><B>trace</B></A> with one or more <I>function-names</I> causes the denoted <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>functions</I></A> to be ``traced.'' Whenever a traced <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>function</I></A> is invoked, information about the call, about the arguments passed, and about any eventually returned values is printed to <A REL=DEFINITION HREF="26_glo_t.htm#trace_output"><I>trace output</I></A>. If <A REL=DEFINITION HREF="#trace"><B>trace</B></A> is used with no <I>function-names</I>, no tracing action is performed; instead, a list of the <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>functions</I></A> currently being traced is returned. <P>
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Invoking <A REL=DEFINITION HREF="#untrace"><B>untrace</B></A> with one or more function names causes those functions to be ``untraced'' (i.e., no longer traced). If <A REL=DEFINITION HREF="#untrace"><B>untrace</B></A> is used with no <I>function-names</I>, all <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>functions</I></A> currently being traced are untraced. <P>
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If a <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>function</I></A> to be traced has been open-coded (e.g., because it was declared <A REL=DEFINITION HREF="d_inline.htm#inline"><B>inline</B></A>), a call to that <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>function</I></A> might not produce trace output. <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 fact (n) (if (zerop n) 1 (* n (fact (- n 1)))))
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=> FACT
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(trace fact)
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=> (FACT)
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;; Of course, the format of traced output is implementation-dependent.
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(fact 3)
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>> 1 Enter FACT 3
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>> | 2 Enter FACT 2
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>> | 3 Enter FACT 1
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>> | | 4 Enter FACT 0
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>> | | 4 Exit FACT 1
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>> | 3 Exit FACT 1
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>> | 2 Exit FACT 2
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>> 1 Exit FACT 6
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=> 6
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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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Might change the definitions of the <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>functions</I></A> named by <I>function-names</I>. <P>
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<P><B>Affected By:</B><P>
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<P>
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Whether the functions named are defined or already being traced. <P>
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<P><B>Exceptional Situations:</B><P>
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<P>
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Tracing an already traced function, or untracing a function not currently being traced, should produce no harmful effects, but might signal a warning. <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_debug_.htm#STtrace-outputST"><B>*trace-output*</B></A>, <A REL=DEFINITION HREF="m_step.htm#step"><B>step</B></A> <P>
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<P><B>Notes:</B><P>
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<P>
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<A REL=DEFINITION HREF="#trace"><B>trace</B></A> and <A REL=DEFINITION HREF="#untrace"><B>untrace</B></A> may also accept additional <A REL=DEFINITION HREF="26_glo_i.htm#implementation-dependent"><I>implementation-dependent</I></A> argument formats. The format of the trace output is <A REL=DEFINITION HREF="26_glo_i.htm#implementation-dependent"><I>implementation-dependent</I></A>. <P>
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Although <A REL=DEFINITION HREF="#trace"><B>trace</B></A> can be extended to permit non-standard options, <A REL=DEFINITION HREF="26_glo_i.htm#implementation"><I>implementations</I></A> are nevertheless encouraged (but not required) to warn about the use of syntax or options that are neither specified by this standard nor added as an extension by the <A REL=DEFINITION HREF="26_glo_i.htm#implementation"><I>implementation</I></A>, since they could be symptomatic of typographical errors or of reliance on features supported in <A REL=DEFINITION HREF="26_glo_i.htm#implementation"><I>implementations</I></A> other than the current <A REL=DEFINITION HREF="26_glo_i.htm#implementation"><I>implementation</I></A>. <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/iss174.htm">FUNCTION-NAME:LARGE</A><P></UL><HR>
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