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We are using the concept of CYK table formation to produce these results on Prolog. Here are some sample outputs for product_c(+Cell1, +Cell2, -Product): 

?- product_c(["A","B"],["C","D"],What).
What = ["AC", "AD", "BC", "BD"].
?- product_c(["A"],[],What).
What = [].

I've tried using string_concat, but that gives me results like:

What = ["A", "B", "C", "D"].

I'm not sure how to go about this problem. Any help is much appreciated.

false
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Bluewater2010
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  • Can you show the code you've written? And some example query/expected result? – damianodamiano Mar 01 '18 at 13:40
  • This is what I did: product_c(Cell1,Cell2,Product) :- append(Cell1, Cell2, Product). Correction: I used append NOT string_concat. And I get What = ["A", "B", "C", "D"] instead of the expected result of What = ["AC", "AD", "BC", "BD"]. – Bluewater2010 Mar 01 '18 at 13:47

2 Answers2

1

So you can solve this problem in this way:

list_pairs(List1, List2,String) :-
    List1 = ["A","B"],
    List2 = ["C","D"],
    findall([X,Y], (member(X, List1), member(Y, List2)), Pairs),
    pairToString(Pairs,String).

pairToString([],[]).
pairToString([[X,Y]|T],[H1|T1]):-
    atomic_list_concat([X,Y], '', Atom),
    atom_string(Atom, H1),
    pairToString(T,T1).

So, with findall/3 you get all the combinations of the two list (Pairs = [["A", "C"], ["A", "D"], ["B", "C"], ["B", "D"]]). To convert this in a list of string, i've written pairToString/2.

?- list_pairs(List1, List2, Pairs).
List1 = ["A", "B"],
List2 = ["C", "D"],
Pairs = ["AC", "AD", "BC", "BD"]
damianodamiano
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1

You got here kind of type mix up. The quickest fix would be like taking the cartesian product from here Cartesian prod and then concatenating the result list. 

list_List_CartProd(L1,L2,L3):- 
     cartProd(L1,L2,L3,L1).

cartProd(_, [], [], _).

cartProd([], [_|T2], L3, L4):-
    cartProd(L4, T2, L3, L4).

cartProd([H1|T1], [H2|T2], [[H1,H2]|T3], L4):-
    cartProd(T1, [H2|T2], T3, L4).

list_concatEl([],[]).
list_concatEl([X|Xs],[Y|Ys]) :-
    X=[X1,X2],
    string_concat(X1,X2,Y),
    list_concatEl(Xs,Ys).

product_c(L1,L2,L4) :-
    list_List_CartProd(L1,L2,L3),
    list_concatEl(L3,L4).

If we test it now with your cases we get:

?- product_c(["A","B"],["C","D"],What).
What = ["AC", "BC", "AD", "BD"] ;
false.

?- product_c(["A"],[],What). 
What = [] ;
false.
Ben373
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  • @repeat Thx for mentioning, I forgot that in Prolog predicates start with an lowercase letter and Variables with Uppercase or underscore. It happenend, because I used different names for the predicates when testing and tried to change them for clarification. Anyway editet it above. – Ben373 Mar 05 '18 at 16:45