Basic Traveling Commands

Causes the debugger to single-step to the very next port.
Causes the debugger to skip, or ignore, the internal details of a procedure's execution. The debugger starts showing goals again when execution returns to the invocation's Done, Exit, Fail, or Exception port. If the debugger is already at the invocation's Done, Exit, Fail, or Exception port, then skipping is meaningless, and the debugger will just creep. Note that skipping is very fast, running at nearly full compiled speed.

One important point about skipping: if the goal you skip over is not determinate, and you later redo (backtrack) into the goal, you will not be able to see the redos into goals that were skipped over. This is because the debugger does not keep any information about the goals that have been skipped over, in order to achieve much greater speed. You will, however, be able to see any new calls that are executed in the process of trying to redo the goal.

Turns off the debugger for the rest of the execution of the top-level goal. When the execution of this goal is completed, the debugger returns to its current mode. This option does not turn the debugger off; to turn the debugger off, you must type "nodebug." at the main Prolog prompt. Like skip, nonstop causes the debugger to run at nearly full compiled speed.