root/trunk/examples/searching/miss_cann.lgt

:- object(miss_cann,
    instantiates(heuristic_state_space)).


    :- info([
        version is 1.1,
        author is 'Paulo Moura',
        date is 2000/11/21,
        comment is 'Missionaries and cannibals heuristic state space search problem.']).


    :- uses(loop, [forto/3]).


    initial_state(start, ((3,3), left, (0,0))).


    goal_state(end, ((0,0), right, (3,3))).


    print_state(((Me,Ce), B, (Md,Cd))) :-
        forto(1, Me, write('M')),
        forto(1, Ce, write('C')),
        (B = left ->
            write('.<__>..........')
            ;
            write('..........<__>.')),
        forto(1, Md, write('M')),
        forto(1, Cd, write('C')),
        nl.


    next_state(((Me,Ce),left,(Md,Cd)), ((Me2,Ce2),right,(Md2,Cd2)), 1) :-  %mm
        Me >= 2,
        once((Me - 2 =:= 0; Me - 2 >= Ce)),
        Cd =< 2,
        Me2 is Me - 2,
        Ce2 is Ce,
        Md2 is Md + 2,
        Cd2 is Cd.

    next_state(((Me,Ce),left,(Md,Cd)), ((Me2,Ce2),right,(Md2,Cd2)), 2) :-  %m
        Me >= 1,
        once((Me - 1 =:= 0; Me - 1 >= Ce)),
        Cd =< 1,
        Me2 is Me - 1,
        Ce2 is Ce,
        Md2 is Md + 1,
        Cd2 is Cd.

    next_state(((Me,Ce),left,(Md,Cd)), ((Me2,Ce2),right,(Md2,Cd2)), 1) :-  %cc
        Ce >= 2,
        once((Md >= Cd + 2;  Md =:= 0)),
        Me2 is Me,
        Ce2 is Ce - 2,
        Md2 is Md,
        Cd2 is Cd + 2.

    next_state(((Me,Ce),left,(Md,Cd)), ((Me2,Ce2),right,(Md2,Cd2)), 2) :-  %c
        Ce >= 1,
        once((Md >= Cd + 1; Md =:= 0)),
        Me2 is Me,
        Ce2 is Ce - 1,
        Md2 is Md,
        Cd2 is Cd + 1.

    next_state(((Me,Ce),left,(Md,Cd)), ((Me2,Ce2),right,(Md2,Cd2)), 1) :-  %mc
        Me >= 1,
        Ce >= 1,
        Md >= Cd,
        Me2 is Me - 1,
        Ce2 is Ce - 1,
        Md2 is Md + 1,
        Cd2 is Cd + 1.

    next_state(((Me,Ce),right,(Md,Cd)), ((Me2,Ce2),left,(Md2,Cd2)), Cost) :-
        next_state(((Md,Cd),left,(Me,Ce)), ((Md2,Cd2),right,(Me2,Ce2)), Cost).


    heuristic(((_, _), _, (Md, Cd)), Cost) :-
        Cost is 6 - (Md + Cd).


:- end_object.