Turn function tracing on or off.
Integer_Type _slangtrace
The _slangtrace variable is a debugging aid that when set to a
non-zero value enables tracing when function declared by
_trace_function is entered. If the value is greater than
zero, both intrinsic and user defined functions will get traced.
However, if set to a value less than zero, intrinsic functions will
not get traced.
_trace_function, _traceback, _print_stack