function-name—a function name.
trace-result—implementation-dependent, unless no function-names are supplied, in which case trace-result is a list of function names.
untrace control the invocation of the trace facility.
trace with one or more function-names causes
the denoted functions to be “traced.”
Whenever a traced function is invoked, information
about the call,
about the arguments passed,
and about any eventually returned values
is printed to trace output.
trace is used with no function-names,
no tracing action is performed;
instead, a list of the functions currently being traced is returned.
untrace with one or more function names causes those
functions to be “untraced” (i.e., no longer traced).
untrace is used with no function-names,
all functions currently being traced are untraced.
If a function to be traced has been open-coded
(e.g., because it was declared
a call to that function might not produce trace output.
(defun fact (n) (if (zerop n) 1 (* n (fact (- n 1))))) → FACT (trace fact) → (FACT) ;; Of course, the format of traced output is implementation-dependent. (fact 3) ▷ 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 → 6
Might change the definitions of the functions named by function-names.
Whether the functions named are defined or already being traced.
Tracing an already traced function, or untracing a function not currently being traced, should produce no harmful effects, but might signal a warning.
untrace may also accept additional
implementation-dependent argument formats. The format of the trace
output is implementation-dependent.
trace can be extended to permit non-standard options,
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 implementation,
since they could be symptomatic of typographical errors
or of reliance on features supported in implementations
other than the current implementation.