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call_explicit(+Goal, +Module)

Succeeds if Goal which is defined in module Module succeeds.

Goal: Atom or compound term.
Module: Atom.

This built-in predicate is obsolete!

Description

This predicate provides a means to override the module system's visibility rules. While the builtins call/1 and call/2 call the predicate that is visible from a certain module, call_explicit/2 allows to call a predicate which is defined in a certain module. This allows calling a predicate that is otherwise not visible in the context module. The most plausible use of this feature is to allow local redefinition of a predicate using the existing definition in the implementation.

Note that call_explicit can only call exported or global predicates in order to preserve module privacy.

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.
(4) instantiation fault: Module is not instantiated.
(5) type error: Goal is neither an atom nor a compound term.
(5) type error: Module is not an atom.
(68) calling an undefined procedure: Goal is an undefined procedure in Module.

Examples

Success:
     [eclipse]: cd(~).
     system interface error:
                      No such file or directory in cd(~)

     [eclipse]: [user].         % redefine cd/1, using its
                              % original definition
      cd(~) :- !,
               getenv('HOME', Home),
               call_explicit(cd(Home), sepia_kernel).
      cd(Dir) :-
               call_explicit(cd(Dir), sepia_kernel).

      [eclipse]: cd(~).
      yes.

Fail:
      call_explicit(fail, sepia_kernel).

Error:
      call_explicit(Var,eclipse).                (Error 4).
      call_explicit(ls,Var).                     (Error 4).
      call_explicit("write(a)",eclipse).         (Error 5).
      call_explicit(foo(a),eclipse).             (Error 68).