Debugging commands

In debugging mode, the system displays a message when a predicate is entered (Call), exited (Exit), reentered (Redo), or has failed (Fail). After a predicate is entered or reentered, the system waits for a command from the users. A command is a single letter followed by a carriage-return, or may simply be a carriage-return. The following commands are available:

• RET - This command causes the system to display a message at each step.
• c - creep, the same as a carriage-return RET.
• l - leap, causes the system to run in the usual mode until a spy-point is reached.
• s - skip, causes the system to run in the usual mode until the predicate is finished (Exit or Fail).
• r - repeat creep, causes the system to creep without asking for further commands from the users.
• a - abort, causes the system to abort execution.
• h or ? - help, causes the system to display available commands and their meanings.
• t - backtrace, prints out the backtrace leading to the current call.
• t i - backtrace, prints out the backtrace from the call numbered i to the current call.
• u - undoes what has been done to the current call, and redoes it.
• u i - undoes what has been done to the call numbered i, and redoes it.
• < - resets the print depth to 10.
• < d - resets the print depth to d.