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Question

I have a lists which contains 2 lists: the first one is a lists of lists and the second one the same. I want to make a list of lists which contains tuples with three elements. This is my initial list :

[ [ [1 2 3 4 a], [aa, bb], R1], [[ 1 3 4 5 b], [X, Y] , R2]] , [anything]] 

I want to obtain this list:

[[a, [aa, bb], R1], [b, [x, y], R2]]

How can I implement a predicate to return me the list above in prolog? I have tried this :

get_game_tiles([[[_,_,_,_,I],[X,Y],R]|Tail], [[Elem1,Elem2|Tail]]) :-
   findall(S,
         (  member(S,[[[_,_,_,_,S], [X,Y], R], [[_,[_]]]]), S = I ),
         [[Elem1,_|_]]),
   findall([A,B],
         (  member([A,B] ,[[[_,_,_,_,S], [A,B], R], [[_,[_]]]]),
            A = X, B = Y
         ) ,
         [[_,Elem2|_]]),
   findall(Z,
         (  member(Z ,[[[_,_,_,_,S], [A,B], Z], [[_,[_]]]]),
            Z = R
         ),
         [[_,_|Tail]]).

Answer 1

Your solution with findall calls is very over-done. There are some issues, such as the following:

member(S,[[[_,_,_,_,S], [X,Y], R], [[_,[_]]]])

and

member(Z ,[[[_,_,_,_,S], [A,B], Z], [[_,[_]]]])

These are a cyclic terms. You're querying whether S is a member of the list, [[[_,_,_,_,S], [X,Y], R], [[_,[_]]]] . S is embedded in a term within an element of the list you are asking if S is a member of. Likewise, you're asking if Z is a member of the list, [[[_,_,_,_,S], [A,B], Z], [[_,[_]]]] . Z is embedded in a term within an element of the list you are asking if Z is a member of.

member([A,B] ,[[[_,_,_,_,S], [A,B], R], [[_,[_]]]])

This isn't so much a problem but will always be false since the list consists of the following elements, neither of which match [A,B] (a list of two elements):

[[_,_,_,_,S], [A,B], R]  % a list of three elements
[[_, [_]]]               % a list of one element ([_, [_]])

Assuming I understand the conditions of your problem (I am not yet convinced 100% that I do), the approach in Prolog is actually much simpler:

get_game_tiles([], []).             % Empty list maps to empty list
get_game_tiles([S|_], []) :-        % List starting with non-matching pattern results in
    S \= [[_,_,_,_,_], [_,_], _]].  %   empty and ends recursion
get_game_tiles([[[_,_,_,_,X], [A,B], R]]|T], [[X, [A,B], R]|TR]) :-
    get_game_tiles(T, TR).