| 1 | |
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| 2 | :- object(queue, |
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| 3 | implements(queuep), |
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| 4 | extends(compound)). |
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| 5 | |
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| 6 | |
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| 7 | :- info([ |
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| 8 | version is 1.0, |
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| 9 | authors is 'Paulo Moura', |
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| 10 | date is 2000/7/24, |
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| 11 | comment is 'Queue predicates implemented using difference lists.']). |
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| 12 | |
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| 13 | |
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| 14 | as_list(Queue-Back, List) :- |
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| 15 | Queue == Back -> |
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| 16 | List = [] |
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| 17 | ; |
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| 18 | List = [Head| Tail], |
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| 19 | Queue = [Head| Rest], |
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| 20 | as_list(Rest-Back, Tail). |
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| 21 | |
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| 22 | |
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| 23 | empty(Front-Back) :- |
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| 24 | Front == Back. |
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| 25 | |
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| 26 | |
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| 27 | head(Front-Back, Head) :- |
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| 28 | Front \== Back, |
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| 29 | Front = [Head| _]. |
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| 30 | |
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| 31 | |
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| 32 | join(Element, Front-[Element| Back], Front-Back). |
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| 33 | |
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| 34 | |
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| 35 | join_all([], Queue, Queue). |
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| 36 | |
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| 37 | join_all([Head| Tail], Queue1, Queue3) :- |
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| 38 | join(Head, Queue1, Queue2), |
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| 39 | join_all(Tail, Queue2, Queue3). |
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| 40 | |
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| 41 | |
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| 42 | jump(Element, Front-Back, [Element| Front]-Back). |
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| 43 | |
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| 44 | |
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| 45 | jump_all([], Queue, Queue). |
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| 46 | |
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| 47 | jump_all([Head| Tail], Queue1, Queue3) :- |
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| 48 | jump(Head, Queue1, Queue2), |
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| 49 | jump_all(Tail, Queue2, Queue3). |
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| 50 | |
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| 51 | |
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| 52 | length(Front-Back, Length) :- |
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| 53 | length(Front, Back, 0, N), |
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| 54 | Length = N. |
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| 55 | |
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| 56 | |
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| 57 | length(Front, Back, N, N) :- |
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| 58 | Front == Back, !. |
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| 59 | |
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| 60 | length([_|Front], Back, K, N) :- |
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| 61 | L is K+1, |
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| 62 | length(Front, Back, L, N). |
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| 63 | |
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| 64 | |
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| 65 | new(Back-Back). |
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| 66 | |
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| 67 | |
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| 68 | serve(OldFront-Back, Head, NewFront-Back) :- |
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| 69 | OldFront \== Back, |
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| 70 | OldFront = [Head| NewFront]. |
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| 71 | |
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| 72 | |
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| 73 | valid(Queue) :- |
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| 74 | nonvar(Queue), |
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| 75 | valid2(Queue). |
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| 76 | |
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| 77 | |
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| 78 | valid2(Queue-Back) :- |
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| 79 | Queue == Back, |
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| 80 | !. |
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| 81 | |
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| 82 | valid2(Queue-Back) :- |
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| 83 | nonvar(Queue), |
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| 84 | Queue = [_| Tail], |
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| 85 | valid2(Tail-Back). |
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| 86 | |
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| 87 | |
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| 88 | :- end_object. |
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