Einstein Riddle with List of terms

Question

I implemented Einstein Riddle in Prolog and I\'m trying to find out who had a fish at home.
I can\'t find fault in this code and trace option is not helping with this pr

Answer 1

You had two errors in your clues - the first you fixed already with the light smoker. The second is that the horse owner lives next to the yellow house, not the green.

Now, my prolog choked on the \+ operator so I recoded your helper predicates. This is what I did:

first(H,[H|_]).

on_the_left(X,Y,[X,Y|_]).
on_the_left(X,Y,[_|Hs]) :- on_the_left(X,Y,Hs).

next_to(X,Y,[X,Y|_]).
next_to(X,Y,[Y,X|_]).
next_to(X,Y,[_|Hs]) :- next_to(X,Y,Hs).

middle(X,[_,_,X,_,_]).

Now the puzzle worked nicely with these clues:

fish(Who) :-
    Houses = [
        house(_Color1, _From1, _Animal1, _Drink1, _Smoke1),
        house(_Color2, _From2, _Animal2, _Drink2, _Smoke2),
        house(_Color3, _From3, _Animal3, _Drink3, _Smoke3),
        house(_Color4, _From4, _Animal4, _Drink4, _Smoke4),
        house(_Color5, _From5, _Animal5, _Drink5, _Smoke5) ],
    first(house(_, norway, _, _, _), Houses), %-- hint 1
    member(house(red, england, _, _, _), Houses), %-- hint 2
    on_the_left(house(green, _, _, _, _), house(white, _, _, _, _), Houses), %-- hint 3 - on_the_left
    member(house(_, denmark, _, tea, _), Houses), %-- hint 4
    next_to(house(_, _, _, _, light), house( _, _, cat, _, _), Houses), %-- hint 5 - next_to
    member(house(yellow, _, _, _, cigar), Houses), %-- hint 6
    member(house(_, germany, _, _, waterpipe), Houses), %-- hint 7
    middle(house(_, _, _, milk, _), Houses), %-- hint 8
    next_to(house(_, _, _, _, light), house(_, _, _, water, _), Houses), %-- hint 9 - next_to
    member(house(_, _, bird, _, nofilter), Houses), %-- hint 10
    member(house(_, sweden, dog, _, _), Houses), %-- hint 11
    next_to(house(_, norway, _, _, _), house(blue, _, _, _, _), Houses), %-- hint 12 - next_to
    next_to(house(_, _, horse, _, _), house(yellow, _, _, _, _), Houses), %-- hint 13 - next_to
    member(house(_, _, _, beer, menthol), Houses), %-- hint 14
    member(house(green, _, _, coffee, _), Houses), %-- hint 15
    member(house(_, Who, fish, _, _), Houses),
    write(Houses), nl.

I got:

[house(yellow, norway, cat, water, cigar), house(blue, denmark, horse, tea, light), house(red, england, bird, milk, nofilter), house(green, germany, fish, coffee, waterpipe), house(white, sweden, dog, beer, menthol)]
germany

Answer 2

just to show an alternative encoding scheme:

solve :- solve(Sol, From), writeln(From), maplist(writeln, Sol).

solve(Sol, From) :-
    phrase( (from(1, norway)
        ,color(red) = from(england)
        ,color(GREEN, green), color(WHITE, white), {GREEN is WHITE-1}
        ,from(denmark) = drink(tea)
        ,smoke(Light, light), animal(Cat, cat), next_to(Light, Cat)
        ,color(Yellow, yellow), smoke(Yellow, cigar)
        ,from(germany) = smoke(waterpipe)
        ,drink(3, milk)
        ,drink(Water, water), next_to(Light, Water)
        ,animal(bird) = smoke(nofilter)
        ,from(sweden) = animal(dog)
        ,from(NORWAY, norway), color(BLUE, blue), next_to(NORWAY, BLUE)
        ,animal(HORSE, horse), next_to(HORSE, GREEN) % next_to(HORSE, Yellow)
        ,drink(beer) = smoke(menthol)
        ,color(green) = drink(coffee)
        ,animal(Fish, fish), from(Fish, From)
    ), [[1,_,_,_,_,_],
        [2,_,_,_,_,_],
        [3,_,_,_,_,_],
        [4,_,_,_,_,_],
        [5,_,_,_,_,_]
    ], Sol).

state(S), [A,B,C,D,E] --> [A,B,C,D,E], {member(S, [A,B,C,D,E])}.

color(A, B)  --> state([A,B,_,_,_,_]).
from(A, B)   --> state([A,_,B,_,_,_]).
animal(A, B) --> state([A,_,_,B,_,_]).
drink(A, B)  --> state([A,_,_,_,B,_]).
smoke(A, B)  --> state([A,_,_,_,_,B]).

X = Y --> {
    X=..[Fx|Ax], Y=..[Fy|Ay],
    Xs=..[Fx,S|Ax], Ys=..[Fy,S|Ay]
}, call(Xs), call(Ys).

next_to(X, Y) --> {1 is abs(X-Y)}.