root/trunk/examples/searching/bridge.lgt

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


    :- info([
        version is 1.1,
        author is 'Paulo Moura',
        date is 2004/8/15,
        comment is 'Bridge puzzle.']).


    :- uses(list, [append/3]).
    :- uses(numberlist, [min/2, max/2]).
    :- uses(set, [insert/3, insert_all/3, select/3]).
    

    initial_state(start, ([], right, [1,3,6,8,12])).


    goal_state(end, ([1,3,6,8,12], left, [])).


    next_state((Left1, left, Right1), (Left2, right, Right2), Slower) :-    % two persons
        append(List, [Person1| Persons], Left1),
        select(Person2, Persons, Others),
        append(List, Others, Left2),
        insert_all([Person1, Person2], Right1, Right2),
        (Person1 > Person2 ->
            Slower = Person1
            ;
            Slower = Person2).

    next_state((Left1, right, Right1), (Left2, left, Right2), Slower) :-    % two persons
        append(List, [Person1| Persons], Right1),
        select(Person2, Persons, Others),
        append(List, Others, Right2),
        insert_all([Person1, Person2], Left1, Left2),
        (Person1 > Person2 ->
            Slower = Person1
            ;
            Slower = Person2).

    next_state((Left1, left, Right1), (Left2, right, Right2), Person) :-    % one person
        select(Person, Left1, Left2),
        insert(Right1, Person, Right2).
        
    next_state((Left1, right, Right1), (Left2, left, Right2), Person) :-    % one person
        select(Person, Right1, Right2),
        insert(Left1, Person, Left2).


    heuristic((Left, Lamp, Right), Heuristic) :-
        Lamp = left ->
            list::min(Left, Heuristic)
            ;
            list::max(Right, Max),
            list::min(Right, Min),
            Heuristic is Max + Min.


    print_state((Left, Lamp, Right)) :-
        write_list(Left),
        (Lamp = left ->
            write(' lamp _|____________|_ ')
            ;
            write(' _|____________|_ lamp ')),
        write_list(Right),
        nl.


    write_list([]).
    
    write_list([Head| Tail]) :-
        write(Head), write(' '),
        write_list(Tail).


:- end_object.