Tracing is a technique used to debug recursive functions. The tracer prints the name of a function and its arguments when it is entered, and its value when it is finished. By tracing certain critical subfunctions, the user can often locate a fault in a large program.
Tracing is controlled by the pseudo-function trace, whose argument is a list of functions to be traced. After trace has been executed, tracing will occur whenever these functions are entered.
When tracing of certain functions is no longer desired, it can be terminated by the pseudo-function untrace whose argument is a list of functions that are no longer to be traced.