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subcall(+Goal, -Delayed_goals)

Succeeds iff Goal succeeds and unifies Delayed_goals with a list of remaining delayed goals.

Goal: Atom or compound term.
Delayed_goals: Variable or list.

Description

Calls the goal Goal. When Goal succeeds, Delayed_goals is unified with a list of goals that were delayed, but not resumed during execution of Goal. These goals, together with the variable bindings in Goal, can be regarded as a qualified answer to Goal. I.e. Goal is true under the condition that the conjunction of delayed goals is also true.

Note that, after exiting from subcall/2, the goals collected in Delayed_goals do no longer exist as delayed goals.

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 neither an atom nor a compound term.
(68) calling an undefined procedure: Goal is an undefined procedure.

Examples

Success:
    [eclipse]: X > 0, subcall(X < 5, DG).

    X = X
    DG = [X < 5]

    Delayed goals:
    X > 0
    yes.
    [eclipse]: subcall( (X > 0, Y > 0, X = 3) , DG).

    Y = Y
    X = 3
    DG = [Y > 0]
    yes.

Fail:
    subcall(fail, _).
Error:
    subcall(Var, D).                (Error 4).
    subcall(3, D).                  (Error 5).
    subcall(foo(a), D).             (Error 68).