Advanced Control Options

These options are described in greater depth in dbg-bas-tra-ccf.

retry -- This option restarts the current invocation. This may be useful when, for example, you find yourself leaving with some incorrect result. When a retry is performed, the invocation counter is reset so that counting will continue from the current invocation number regardless of what happened before the retry. This is in accord with the fact that execution has returned to the state it was in at the time of the original call. The message
          % Retrying goal

is displayed to indicate where this occurred, in case you wish to follow these numbers later.

r i
retry previous invocation -- If you supply an integer after the retry command, then this is taken as specifying an invocation number and the system tries to get you to the Call port, not of the current box, but of the invocation box you have specified. This must be an ancestor invocation.
fail -- This is similar to Retry except that it transfers control to the Fail port of the current box. This places your execution in a situation in which it is about to backtrack out of the current invocation, having failed the goal.
f i
fail previous invocation -- This is similar to r i except that it transfers control to the Fail port of the invocation specified (which must be an ancestor).