89 lines
1.3 KiB
Plaintext
89 lines
1.3 KiB
Plaintext
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:- object(queue,
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implements(queuep),
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extends(compound)).
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:- info([
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version is 1.0,
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authors is 'Paulo Moura',
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date is 2000/7/24,
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comment is 'Queue predicates implemented using difference lists.']).
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as_list(Queue-Back, List) :-
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Queue == Back ->
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List = []
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;
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List = [Head| Tail],
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Queue = [Head| Rest],
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as_list(Rest-Back, Tail).
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empty(Front-Back) :-
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Front == Back.
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head(Front-Back, Head) :-
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Front \== Back,
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Front = [Head| _].
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join(Element, Front-[Element| Back], Front-Back).
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join_all([], Queue, Queue).
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join_all([Head| Tail], Queue1, Queue3) :-
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join(Head, Queue1, Queue2),
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join_all(Tail, Queue2, Queue3).
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jump(Element, Front-Back, [Element| Front]-Back).
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jump_all([], Queue, Queue).
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jump_all([Head| Tail], Queue1, Queue3) :-
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jump(Head, Queue1, Queue2),
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jump_all(Tail, Queue2, Queue3).
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length(Front-Back, Length) :-
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length(Front, Back, 0, N),
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Length = N.
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length(Front, Back, N, N) :-
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Front == Back, !.
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length([_|Front], Back, K, N) :-
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L is K+1,
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length(Front, Back, L, N).
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new(Back-Back).
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serve(OldFront-Back, Head, NewFront-Back) :-
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OldFront \== Back,
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OldFront = [Head| NewFront].
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valid(Queue) :-
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nonvar(Queue),
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valid2(Queue).
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valid2(Queue-Back) :-
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Queue == Back,
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!.
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valid2(Queue-Back) :-
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nonvar(Queue),
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Queue = [_| Tail],
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valid2(Tail-Back).
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:- end_object.
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