[ Control | Reference Manual | Alphabetic Index ]

call(+Goal)

Succeeds if Goal succeeds.

Goal: Atom or compound term.

Description

Calls the goal Goal. This predicate is used to call goals whose functors are known only at the time they are called.

Note that:

call(Goal) is logically the same as Goal and !/0 does not cut through call/1.

Modules

This predicate is sensitive to its module context (tool predicate, see @/2).

Fail Conditions

Fails if Goal fails

Resatisfiable

Resatisfiable if Goal is resatisfiable

Exceptions

(4) instantiation fault: Goal is not instantiated.
(5) type error: Goal is not an atom or a compound term.

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->write(here),true).
      yes.

Fail:
      [eclipse]: call(fail),write(here).
      no.
Error:
      call(G).                  (Error 4).
      call("write(a)").         (Error 5).