Jan Burse, created Oct 19. 2019
* When a goal belonging to a defined predicate is invoked a new
* frame is created. When the interpreter encounters a cut (!) it
* will remove all choice points inside this frame. The cut (!) will
* also remove choice points that were created by disjunction (;)/2.
* On these grounds the predicate (;)/2 is called cut transparent.
* ?- X = a; X = b.
* X = a ;
* X = b
* ?- X = a, !; X = b.
* X = a
* Some of the predefined logical predicates are cut transparent in
* all arguments. This includes the predicates (,)/2 and (;)/2.
* Others are only cut transparent in the second argument. This
* includes the predicates (->)/2 and (*->)/2. Other predicates,
* such as call/1, once/1 and (\+)/1, are not cut transparent at all.
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* A; B: [ISO 7.8.6]
* The predicate succeeds whenever A or B succeeds. Both goal
* arguments A and B are cut transparent.
* A -> B;C: [ISO 7.8.8]
* The predicate succeeds when A succeeds and then whenever B succeeds, or
* else whenever C succeeds. Only the goal arguments B and C are
* cut transparent.
* A *-> B; C:
* The predicate succeeds whenever A and B succeed, or else if B didn’t
* succeed whenever C succeeds. Only the goal arguments B and C are
* cut transparent.
% +Goal ; +Goal
_; _ :- throw(
body, ;/2), _)).
* A -> B: [ISO 7.8.7]
* The predicate succeeds when A succeeds and then whenever B
* succeeds. Only the goal argument B is cut transparent.
% +Goal -> +Goal
_ -> _ :- throw(
body, -> /2), _)).
* A *-> B:
* The predicate succeeds whenever A and B succeed. Only the goal
* argument B is cut transparent.
% +Goal *-> +Goal
_ *-> _ :- throw(
body, *-> /2), _)).
* repeat: [ISO 8.15.3]
* The predicate succeeds repeatedly.