Deterministic predicates are predicates that must succeed exactly
once and, for well behaved predicates, leave no choicepoints. Typically
they have zero or more input- and zero or more output arguments. The
test goal supplies proper values for the input arguments and verifies
the output arguments. Verification can use test-options or be explicit
in the body. The tests in the example below are equivalent.
test(add) :-
A is 1 + 2,
A =:= 3.
test(add, [true(A =:= 3)]) :-
A is 1 + 2.
The test engine verifies that the test-body does not leave a
choicepoint. We illustrate that using the test below:
test(member) :-
member(b, [a,b,c]).
Although this test succeeds, member/2
leaves a choicepoint which is reported by the test subsystem. To make
the test silent, use one of the alternatives below.
test(member) :-
member(b, [a,b,c]), !.
test(member, [nondet]) :-
member(b, [a,b,c]).
