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suspension_to_goal(+Susp, ?Goal, ?Module)

Succeeds for an unwoken suspension and returns the corresponding Goal structure and caller module.

+Susp: A suspension.
?Goal: A variable or a callable term.
?Module: A variable or a module.

This built-in predicate is obsolete!

Description

This built-in is used to access the contents of the abstract suspension data type. It is complementary to make_suspension/2 as it returns the original goal structure and the module where make_suspension/2 was executed. If applied to an already woken suspension it fails.

Note that a suspension is not a standard Prolog data structure and can only be manipulated in a restricted way. In particular, a suspension is not a term with functor 'GOAL' or 'WOKEN GOAL' although it is printed this way by default. suspension_to_goal/3 is the only way to access the contents of a suspension.

Fail Conditions

Fails if the suspension is already woken.

Resatisfiable

No.

Exceptions

(4) instantiation fault: Susp is not instantiated.
(5) type error: Susp is not a suspension.
(5) type error: Goal is neither variable nor a callable term.
(5) type error: Module is neither variable nor atom.

Examples

[eclipse 1]: make_suspension(writeln(hello),S),
        suspension_to_goal(S, Goal, Module).
S = 'GOAL'(writeln(hello), eclipse)
Goal = writeln(hello)
Module = eclipse
Delayed goals:
        writeln(hello)
yes.
[eclipse 2]: make_suspension(writeln(hello),S),
        call_suspension(S),
        suspension_to_goal(S, Goal, Module).
hello

no (more) solution.