Prolog separating into two lists issue

Question

I have a prolog assignment.

I need to look at the first item in a list, see if its following items are the same until they are not and separate the lists by the firs

Answer 1

Here is another solution that takes into account what @Sarah wrote. Given this use, grab/3 should never succeed for an empty list for the first or second argument.

grab([A], [A], []).
grab([A,B|Bs], [A], [B|Bs]) :-
   dif(A,B).
grab([A,A|Xs], [A|As], Bs) :-
   grab([A|Xs], As, Bs).

?- Xs = [A,B], grab(Xs,Ys,Zs).
  Xs = [A, B], Ys = [A],    Zs = [B], dif(A, B)
; Xs = Ys,     Ys = [B, B], Zs = [],  A = B
; false.