root/trunk/examples/searching/farmer.lgt

:- object(farmer,
    instantiates(state_space)).


    :- info([
        version is 1.0,
        author is 'Paulo Moura',
        date is 1998/3/23,
        comment is 'Farmer, cabbage, goat, and wolf state space search problem.']).


    initial_state(start, (north, north, north, north)).


    goal_state(end, (south, south, south, south)).


    next_state((Cabbage, Goat, Wolf, Farmer), (FCabbage, Goat, Wolf, FFarmer)) :-
        same_side(Farmer, Cabbage),
        \+ same_side(Goat, Wolf),
        flip(Farmer, FFarmer),
        flip(Cabbage, FCabbage).

    next_state((Cabbage, Goat, Wolf, Farmer), (Cabbage, FGloat, Wolf, FFarmer)) :-
        same_side(Farmer, Goat),
        flip(Farmer, FFarmer),
        flip(Goat, FGloat).

    next_state((Cabbage, Goat, Wolf, Farmer), (Cabbage, Goat, FWolf, FFarmer)) :-
        same_side(Farmer, Wolf),
        \+ same_side(Cabbage, Goat),
        flip(Farmer, FFarmer),
        flip(Wolf, FWolf).

    next_state((Cabbage, Goat, Wolf, Farmer), (Cabbage, Goat, Wolf, FFarmer)) :-
        \+ same_side(Cabbage, Goat),
        \+ same_side(Goat, Wolf),
        flip(Farmer, FFarmer).


    flip(north, south).
    
    flip(south, north).


    same_side(north, north).

    same_side(south, south).


    print_state((Cabbage, Goat, Wolf, Farmer)) :-
        (Cabbage = north -> write(c); write('_')),
        (Goat = north -> write(g); write('_')),
        (Wolf = north -> write(w); write('_')),
        (Farmer = north -> write('f.<__>.........._'); write('_..........<__>.f')),
        (Cabbage = north -> write('_'); write(c)),
        (Goat = north -> write('_'); write(g)),
        (Wolf = north -> write('_'); write(w)),
        nl.


:- end_object.