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engine_resume(+Engine, ?Term, -Status)

Resume execution of an engine
Engine
An engine handle
Term
A term passed to the engine
Status
Status term returned from the engine

Description

Resume execution of the given engine, and return with a status code once execution has stopped. The computation is performed by the same thread that is calling engine_resume/3.

This predicate can be used with any engine, independent of whether the engine was created with or without the 'thread' option.

For details about the returned Status, see get_engine_property/3. All status codes except 'running' are possible.

Term is an arbitrary term, a copy of which is is passed to the resumed engine. The way the resumed engine interprets Term depends on its status at resumption time:

false and exception(_)
Term is interpreted as a goal, and called. This is the case for a newly created engine.
true
Term is also interpreted as a goal and called, but it forms a conjunction with the previously succeeded goals (i.e. if it fails, it backtracks into the goal given in the previous resume).
yielded(_)
Term is unified with the second argument of the yield/2 call in which the engine was stopped.
flushio(_) and waitio(_)
Term is ignored.
exited(_)
Engine cannot be resumed (error).
In the cases where Term is executed as a goal, note that the engine works on a copy of Term, therefore any variable bindings performed by the engine will not be visible to the caller of engine_resume/3. Any results must be returned explicitly, either via yield/2, via stream communication, or via nonlogical storage.

Modes and Determinism

Modules

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

Exceptions

(4) instantiation fault
Engine is not instantiated
(5) type error
Engine is not an engine handle
(180) engine not ready
Engine is busy (running)
(182) engine dead/exited
Engine dead/exited

Examples

    ?- engine_create(E, []), engine_resume(E, writeln(hello), S).
    hello
    E = $&(engine,"376oe7")
    S = true
    Yes (0.00s cpu)

    ?- engine_create(E, [thread]), engine_resume(E, writeln(hello), S).
    hello
    E = $&(engine,"376oe7")
    S = true
    Yes (0.00s cpu)

    ?- engine_create(E, []), engine_resume(E, 3=4, S).
    E = $&(engine,"376oe7")
    S = false
    Yes (0.00s cpu)

    ?- engine_create(E, []), engine_resume(E, throw(ball), S).
    E = $&(engine,"376oe7")
    S = exception(ball)
    Yes (0.00s cpu)

    ?- engine_create(E, []), engine_resume(E, throw(ball), S).
    E = $&(engine,"376oe7")
    S = exception(ball)
    Yes (0.00s cpu)

    ?- engine_create(E, []),
       engine_resume(E, (member(X,[a,b]),writeln(X)), S1),
       writeln(first_resume->S1),
       engine_resume(E, fail, S2),
       writeln(second_resume->S2),
       engine_resume(E, fail, S3),
       writeln(third_resume->S3).
    a
    first_resume -> true
    b
    second_resume -> true
    third_resume -> false

See Also

engine_create / 2, engine_resume_thread / 2, get_engine_property / 3