is an option for Trace and related functions which specifies when tracing should be switched on.


  • With the setting TraceOn->patt, Trace and related functions do not start tracing until they encounter expressions to evaluate which match the pattern patt. This pattern is also tested against tags associated with the evaluation.
  • TraceOff can be used within tracing switched on by TraceOn.
  • Once tracing has been switched off by TraceOff, however, TraceOn will not switch it on again.
  • During the execution of Trace, the settings for TraceOn and TraceOff can be modified by resetting the values of the global variables $TraceOn and $TraceOff.


Basic Examples  (1)

Trace evaluation of an expression that evaluates a function g:

Trace only evaluation inside of g:

Introduced in 1991