I know I can do X is random(10). to get a random number from 0 to 10, but is there a similar command to get a random matching item?
Answer
SWI-Prolog v6 has random_member/2 defined like this:
?- listing(random_member).
random:random_member(D, A) :-
length(A, B),
C is random(B),
nth0(C, A, D).
Usage example:
?- random_member(a(N), [a(1), a(2), b(3)]).
N = 1.
?- random_member(a(N), [a(1), a(2), b(3)]).
N = 1.
?- random_member(a(N), [a(1), a(2), b(3)]).
N = 2.
?- random_member(a(N), [a(1), a(2), b(3)]).
false.
?- random_member(a(N), [a(1), a(2), b(3)]).
false.
?- random_member(a(N), [a(1), a(2), b(3)]).
N = 2.
You probably want to use it in the (-,+) mode though.