[ Control | The ECLiPSe Built-In Predicates | Reference Manual | Alphabetic Index ]

!

Cut - succeeds and removes all choice points between cut and parent goal.

Description

The cut operation succeeds immediately when first encountered as a goal. The cut commits all the choices made since the parent goal was invoked, and causes any other alternatives to be discarded.

Note that:

!/0 cuts through ,/2, ;/2 and ->/2, but it does not cut through call/1, not/1 or once/1.

Modes and Determinism

Examples

Success:
      [eclipse]: [user].
       or(A -> B, C) :- call(A), !, call(B).
       or(_ -> _, C) :- call(C).
       user compiled 412 bytes in 0.02 seconds
      [eclipse]: or(write(a)->fail, write(k)).
      a
      no.
      [eclipse]: or(fail->fail,write(k)).
      k
      yes.

      [eclipse]: [user].
       echo :- repeat, read(X), echo(X), !.
       echo(end_of_file).
       echo(X) :- writeln(X), fail.
       user compiled 404 bytes in 0.02 seconds
      yes.    % if the cut is left out, backtracking occurs.
      [eclipse]: echo.
       f(1,2).
      f(1,2)
       end_of_file.
      yes.



See Also

fail / 0, once / 1, repeat / 0, ; / 2