Execution modes

There are two execution modes: usual mode and debugging mode. The query

      trace

switches the execution mode to the debugging mode, and the query

      notrace

switches the execution mode back to the usual mode. In debugging mode, it is possible to trace the execution of asserted and consulted clauses. Compiled code can also be traced if the code is generated when the Prolog flag compiling has the value debugcode.

In order to trace part of the execution of a program, use spy to set spy points.

      spy(Atom/Arity).

The spy points can be removed by

      nospy

In order to remove only one spy point, use

      nospy(Atom/Arity)