Predicate to unzip a list

Question

List1=[(x,1),(y,1),(z,1)]

I\'m attempting to split this list:

into two lists:

List3=[x,y,z]
List4=[1,1,1]

So

Answer 1

You're matching the tuple as a whole, rather than it's component parts.

You should match on [(X1,Y1)|XS], instead of [X|XS] and [Y|Ys].

splt([],[],[]).
splt([(X1,Y1)|Xs],[X1|T1],[Y1|T2]):-
  splt(Xs,T1,T2).

Here the first term is used as input, the second and third as output.

Ideone example, using SWI-Prolog, here.