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cl:macros:trace [2019/12/05 03:00]
cl:macros:trace [2020/07/13 22:00] (current)
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 +====== Macro TRACE, UNTRACE ======
 +  * **trace** //​function-name''​*''//​ → //​trace-result//​
 +  * **untrace** //​function-name''​*''//​ → //​untrace-result//​
 +====Arguments and Values====
 +  * //​function-name//​ - a //​[[CL:​Glossary:​function name]]//.
 +  * //​trace-result//​ - //​[[CL:​Glossary:​implementation-dependent]]//,​ unless no //​[[CL:​Glossary:​function name|function-names]]//​ are supplied, in which case //​trace-result//​ is a //​[[CL:​Glossary:​list]]//​ of //​[[CL:​Glossary:​function names]]//.
 +  * //​untrace-result//​ - //​[[CL:​Glossary:​implementation-dependent]]//​.
 +**trace** and **untrace** control the invocation of the trace facility.
 +Invoking **trace** with one or more //​function-names//​ causes the denoted //​[[CL:​Glossary:​function|functions]]//​ to be "​traced"​. Whenever a traced //​[[CL:​Glossary:​function]]//​ is invoked, information about the call, about the arguments passed, and about any eventually returned values is printed to //​[[CL:​Glossary:​trace output]]//. If **trace** is used with no //​function-names//,​ no tracing action is performed; instead, a list of the //​[[CL:​Glossary:​functions]]//​ currently being traced is returned.
 +Invoking **untrace** with one or more function names causes those functions to be "​untraced"​ (i.e. no longer traced).
 +If **untrace** is used with no //​function-names//,​ all //​[[CL:​Glossary:​function|functions]]//​ currently being traced are untraced.
 +If a //​[[CL:​Glossary:​function]]//​ to be traced has been open-coded (//e.g.// because it was declared **[[CL:​Declarations:​inline]]**),​ a call to that //​[[CL:​Glossary:​function]]//​ might not produce trace output.
 +([[CL:​Macros:​defun]] fact (n)
 +  ([[CL:​Special Operators:​if]] ([[CL:​Functions:​zerop]] n)
 +      1
 +      ([[CL:​Functions:​math-multiply|*]] n (fact ([[CL:​Functions:​math-subtract|-]] n 1))))) <​r>​FACT</​r>​
 +(trace fact) <​r>​(FACT)</​r>​
 +(fact 3)
 +<o>1 Enter FACT 3
 +| 2 Enter FACT 2
 +| 3 Enter FACT 1
 +| | 4 Enter FACT 0
 +| | 4 Exit FACT 1
 +| 3 Exit FACT 1
 +| 2 Exit FACT 2
 +1 Exit FACT 6</o>
 +Of course, the format of traced output is implementation-dependent.
 +====Side Effects====
 +Might change the definitions of the //​[[CL:​Glossary:​functions]]//​ named by //​function-names//​.
 +====Affected By====
 +Whether the functions named are defined or already being traced.
 +====Exceptional Situations====
 +Tracing an already traced function, or untracing a function not currently being traced, should produce no harmful effects, but might signal a warning.
 +====See Also====
 +**[[CL:​Variables:​star-trace-output-star|Variable *TRACE-OUTPUT*]]**,​ **[[CL:​Macros:​step|Macro STEP]]**
 +**trace** and **untrace** may also accept additional //​[[CL:​Glossary:​implementation-dependent]]//​ argument formats. The format of the trace output is //​[[CL:​Glossary:​implementation-dependent]]//​.
 +Although **trace** can be extended to permit non-standard options, //​[[CL:​Glossary:​implementation|implementations]]//​ 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 //​[[CL:​Glossary:​implementation]]//,​ since they could be symptomatic of typographical errors or of reliance on features supported in //​[[CL:​Glossary:​implementation|implementations]]//​ other than the current //​[[CL:​Glossary:​implementation]]//​.