Jan Burse, erstellt 06. Jun 2018
* The predicates call_cleanup/2 and setup_call_cleanup/3 install a
* choice point with a clean-up goal. During a cut the current bindings
* are visible to the clean-up goal. During an exception the bindings
* are undone before invoking the clean-up goal. The latter ternary
* predicate differs from the ISO proposal in that it aggregate_alls
* errors and in that it throws an error when the clean-up goal fails.
* The former binary predicate is not part of the ISO proposal.
* ?- call_cleanup((X = 1; X = 2), (write(X), write(' '))).
* X = 1 ;
* 2 X = 2
* ?- call_cleanup((X = 1; X = 2), (write(X), write(' '))), !.
* 1 X = 1
* Situations might demand that a secondary thread controls a primary
* thread. The program-ming interface allows raising a soft signal in
* a primary Prolog thread from a secondary thread. The method for this
* purpose is setSignal(). The effect on the primary Prolog thread will
* be that the signal message is thrown as an error the first possible
* moment a call port is reached.
* The primary Prolog thread might be in a blocking operation. Therefore
* the method setSignal() also interrupts the primary Prolog thread. The
* operations of the method setSignal() are disabled as long as the mask
* flag is set to false. The mask flag can be read off from the
* corresponding Prolog flag. It can be temporarily reset by the
* system predicate sys_atomic/1.
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* The predicate creates a choice point and succeeds once. The goal
* A is called upon redo or when the choice point is removed.
sys_cleanup/1, 'SpecialSignal', 1).
* call_cleanup(B, C):
* The predicate succeeds whenever B succeeds. Additionally the
* clean-up C is called when B fails or deterministically succeeds.
* The clean-up C is also called when a cut or an exception happens
* inside B or in the continuation.
% call_cleanup(+Goal, +Goal)
* The predicate succeeds whenever A succeeds. The goal A is
* invoked with the signal mask temporarily set to off.
sys_atomic/1, 'SpecialSignal', 0).
* setup_call_cleanup(A, B, C):
* The predicate succeeds when the setup A succeeds once and whenever
* B succeeds. Additionally the clean-up C is called when B fails or
* deterministically succeeds. The clean-up C is also called when a
* cut or an exception happens inside B or in the continuation. The
* setup A and the clean-up C are called with the signal mask temporarily
* set to off.
% setup_call_cleanup(+Goal, +Goal, +Goal)