What's wrong with my prolog program for solving the 3 jugs of water puzzle?

Question

Can anyone find why I can\'t have any true answers with my \'go\' at this code? For example, I write go(7,3,l) and I suppose that it should move 3 litres of water t

Answer 1

Well so as I said in my comment, I kinda wouldn't know how to help you with your current work since there are so many wrong things in it. I'd advise you to read a nice tutorial about Prolog (such as Learn Prolog now) so that you can grab the language basics. Here is a simple way to solve your problem if you're interested. If you don't want your problem to be spoiled, just don't read further : ] (the one I posted is about a 3/5/8 jugs and a 4/4 split).

go(Path) :-
    solve([0-3, 0-5, 8-8], [], [], Temp),
    reverse(Temp, Path).

solve(State, _Visited, Path, Path) :-
    equivalent(State, [0-3, 4-5, 4-8]).
solve(State, Visited, Acc, Path) :-
    move(State, NewState),
    NewState = [_-From, _-To|_],
    forall(member(Past, Visited), \+ equivalent(Past, NewState)),
    solve(NewState, [NewState|Visited], [From-To|Acc], Path).

equivalent(State1, State2) :-
    forall(member(X, State1), member(X, State2)).

move(State, [NewX-From, NewY-To|NewRest]) :-
    select(X-From, State, Rest),
    X \== 0,
    select(Y-To, Rest, NewRest),
    Fillable is To - Y,
    ToFill is min(X, Fillable),
    NewY is Y + ToFill,
    NewX is X - ToFill.

If you need explanations about the code once you've read a little more about prolog, don't hesitate!