CODEWITHSUNDEEP
prolog
BBKING
BBKING

Reputation: 71

Prolog predicates involving lists

I want to write a predicate that finds a particular element in a list, by comparing the lists. For example the data I could have for instance could be like:

likes(phil, [apple, banana, orange]).
likes(hetti, [apple, cherry, grapes]).

etc.

I just want someone to explain how something like this would work, because I've been trying to use member or select; but it seems to be more difficult to find information on this. Could I use pattern matching?

Upvotes: 0

Views: 60

Answers (1)

Enigmativity
Enigmativity

Reputation: 117175

It seems likely that you want to know what the common likes are between phil and hetti. If so, then this is the code:

?- bothlike(phil, hetti, Ls), write(Ls), nl.

bothlike(X, Y, Ls) :-
    likes(X, Xs), 
    likes(Y, Ys), 
    intersection(Xs, Ys, Ls).

likes(phil, [apple, banana, orange]).
likes(hetti, [apple, cherry, grapes]).

intersection([], _, []).
intersection([H1|T1], L2, L3) :-
        member(H1, L2),
        !,
        L3 = [H1|T3],
        intersection(T1, L2, T3).
intersection([_|T1], L2, L3) :-
        intersection(T1, L2, L3).

It gives the answer [apple].

Upvotes: 0

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