Tracing: trace.ss

This library mimics the tracing facility available in Chez Scheme .

Tracing does not respect tail calls; i.e., tracing a procedure that ends with a tail call checks the call so that it executes (and prints) as a non-tail call. Untracing a procedure restores its tail call behavior. Only one procedure can be traced for any single name across all namespaces.

(trace name )

This form takes a sequence of global variables names; each name must be defined as as procedure in the current namespace when the trace expression is evaluated. Each name provided to trace is then redefined to a new procedure. This new procedure traces procedure-calls and procedure-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, this is 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 macro can be used on a name that is already traced in the current namespace. In this case, assuming that the name has not been redefined, trace has no effect. If the name has been redefined, then a new trace is installed. If trace is used on the same name in two different eventspaces, then the first installed trace will remain intact but it will no longer be recognized by the trace and untrace forms.

The value of a trace expression is the list of names specified for tracing.

(untrace name )

This form undoes the effects of the trace form for each name, but only if the current definition of name is the one previously installed by trace. If the current definition for name is not the procedure installed by trace, then the definition is not changed.

The value of an untrace expression is the list of names restored to their untraced definitions.