Question

basically what I’ve managed to do is create a list of tuples in the form A = [[1,2,3],[1,2,12],[1,2,5]] using a fact makelist(A).

What I want to do now is to use that to create another list where it only contains the tuples that are true for a given fact.

for example, I have a test that returns true if a number is prime prime(N) (which takes a number and returns true if it is prime) i want to use that to keep only the third elements in A that are prime. So A = [[1,2,3],[1,2,5]]

I’ve tried to use predsort but that seems to not work on only one element. I thought that it could be done using exclude but I can’t seem to get it to work.

Thanks for any help you can give me.

Answer 1

With lambda.pl, you could write:

:- [lambda].
filter_third_prime(Lists, Result) :-
    include(\[_, _, X|_]^prime(X), Lists, Result).

Without it you could write:

filter_third_prime2(Lists, Result) :-
    include(third_is_prime, Lists, Result).
third_is_prime([_, _, X|_]) :-
    prime(X).

BTW, you mentionned using exclude/3: those solutions are exactly alike ones using it, only they use its dual predicate, include/3.