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Predicate once/1
Availability:built-in
Source[ISO]once(:Goal)
Make a possibly nondet goal semidet, i.e., succeed at most once. Defined as: 
once(Goal) :-
    call(Goal), !.

once/1 can in many cases be replaced with ->/2. The only difference is how the cut behaves (see !/0). The following two clauses below are identical. Be careful about the interaction with ;/2. The library(apply_macros) library defines an inline expansion of once/1, mapping it to (Goal->true;fail). Using the full if-then-else constructs prevents its semantics from being changed when embedded in a ;/2 disjunction. 

1) a :- once((b, c)), d.
2) a :- b, c -> d.
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LogicalCaptain said (2020-05-05T08:09:40):0 upvotes 0 0 downvotes
Picture of user LogicalCaptain.

Definitely prefer once/1 over ->/2. It makes the intent clear and, unlike ->/2, is actually readable.

Example

An example of a predicate which sometimes fails and sometimes succeeds with 1 or more solutions: 50 tries to generate a random number from [1..100] which must be in [3,4,5]:

?- (between(1,50,X),random_between(1,100,R),member(R,[3,4,5])). X = 15, R = 3 ; false.

Using once/1 on this:

?- once((between(1,50,X),random_between(1,100,R),member(R,[3,4,5]))).
X = 17,
R = 3.

?- once((between(1,50,X),random_between(1,100,R),member(R,[3,4,5]))).
X = R, R = 5.

?- once((between(1,50,X),random_between(1,100,R),member(R,[3,4,5]))).
X = 49,
R = 5.

?- once((between(1,50,X),random_between(1,100,R),member(R,[3,4,5]))).
false.

Where is twice/1 ?

If there is a once/1, there should probably be a twice/1 etc.

And there is: limit/2 from library(solution_sequences)