Jan Burse, erstellt 10. Mär 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
* the choice points inside the frame. To instruct the interpreter that
* cuts can nevertheless propagate a defined predicate can be marked as
* cut transparent via the predicate property sys_nobarrier/1.
* ?- 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 a few arguments. This includes the predicates
* (->)/2 and (*->)/2, and also the special forms in connection with the
* predicate (;)/2. Others are not cut transparent at all. This includes
* the predicates sys_call/1, call/1, once/1 and (\+)/1.
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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
% sys_cond(+Goal, +Goal, +Goal)
% sys_soft_cond(+Goal, +Goal, +Goal)
* The predicate marks the choice point of the direct parent, if there is any
* at all, as non-redo able and then succeeds once.
sys_soft_local_cut/0, 'SpecialLogic', 1).
* 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
* The predicate removes pending choice points between the direct parent
* goal invocation and this goal and then succeeds once.
sys_local_cut/0, 'SpecialLogic', 0).
* A *-> B:
* The predicate succeeds whenever A and B succeed. Only the goal
* argument B is cut transparent.
% +Goal *-> +Goal
* The predicate succeeds whenever A succeeds. The goal
* argument A is not converted before calling.
* repeat: [ISO 8.15.3]
* The predicate succeeds repeatedly.