Prolog：如何更改组合（N，[H | T]，P）的输出以返回对列表，而不是;之前的第一个？

Question

Prolog: How can I change the output of combinations(N, [H|T], P) to return a list of pairs, rather than just the first one before ; ? The program works well as long as I press ; in the command line, but I want to return directly a list of pairs.

comb(1, [H|_], [H]).
comb(N, [H|T], [H|C]) :- N1 is N - 1, N1 > 0, comb(N1, T, C).
comb(N, [_|T], C):- comb(N, T, C).

This is my program. Thank you very much!

Answer 1

You are looking for findall/3 .

findall(+Template, :Goal, -Bag)

Create a list of the instantiations Template gets successively on backtracking over Goal and unify the result with Bag . Succeeds with an empty list if Goal has no solutions. findall/3 is equivalent to bagof/3 with all free variables bound with the existential operator ( ^ ), except that bagof/3 fails when Goal has no solutions.

Example:

?- findall(X, comb(2, [a,b,c,d], X), Xs).
Xs = [[a, b], [a, c], [a, d], [b, c], [b, d], [c, d]].