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yap-6.3/Logtalk/examples/searching/breadth_first1.lgt

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:- object(breadth_first(Bound),
instantiates(blind_search(Bound))).
:- info([
version is 1.0,
author is 'Paulo Moura',
date is 1998/3/23,
comment is 'Breadth first state space search strategy.',
parnames is ['Bound']]).
:- uses(list).
search(Space, State, Bound, Solution) :-
breadt(Space, l(State), Bound, Path),
list::reverse(Path, Solution).
breadt(Space, Tree, Bound, Solution) :-
expand([], Tree, Tree2, Solved, Solution, Space, Bound),
(Solved ->
true
;
breadt(Space, Tree2, Bound, Solution)).
expand(Path, l(State), _, true, [State| Path], Space, _) :-
Space::goal_state(State).
expand(Path, l(State), t(State, Subs), fail, _, Space, Bound) :-
Bound > 0,
bagof(l(Next),
(Space::next_state(State, Next),
\+ list::member(Next, [State| Path])),
Subs).
expand(Path, t(State,Subs), t(State, Subs2), Solved, Solution, Space, Bound) :-
expandall([State| Path], Subs, [], Subs2, Solved, Solution, Space, Bound).
expandall(_, [], [Tree| Trees], [Tree| Trees], fail, _, _, _).
expandall(Path, [Tree| Trees], Trees2, Subs2, Solved, Solution, Space, Bound) :-
Bound > 0,
Bound2 is Bound -1,
expand(Path, Tree, Tree2, Solved2, Solution, Space, Bound2),
(Solved2 ->
Solved = true
;
expandall(Path, Trees, [Tree2| Trees2], Subs2, Solved, Solution, Space, Bound))
;
expandall(Path, Trees, Trees2, Subs2, Solved, Solution, Space, Bound).
:- end_object.