The mzlib/trace library mimics the tracing facility available in Chez Scheme.
(trace id ) |
Each id must be bound to a procedure in the environment of the trace expression. Each id is set!ed to a new procedure that traces procedure calls and returns by printing the arguments and results of the call. If multiple values are returned, each value is displayed starting on a separate line.
When traced procedures invoke each other, nested invocations are shown by printing a nesting prefix. If the nesting depth grows to ten and beyond, a number is printed to show the actual nesting depth.
The trace form can be used on an identifier that is already traced. In this case, assuming that the variable’s value has not been changed, trace has no effect. If the variable has been changed to a different procedure, then a new trace is installed.
Tracing respects tail calls to preserve loops, but its effect may be visible through continuation marks. When a call to a traced procedure occurs in tail position with respect to a previous traced call, then the tailness of the call is preserved (and the result of the call is not printed for the tail call, because the same result will be printed for an enclosing call). Otherwise, however, the body of a traced procedure is not evaluated in tail position with respect to a call to the procedure.
The result of a trace expression is #<void>.
(untrace id ) |
Undoes the effects of the trace form for each id, set!ing each id back to the untraced procedure, but only if the current value of id is a traced procedure. If the current value of a id is not a procedure installed by trace, then the variable is not changed.
The result of an untrace expression is #<void>.