84 lines
1.4 KiB
Plaintext
84 lines
1.4 KiB
Plaintext
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:- object(location(_X, _Y)).
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:- info([
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authors is 'Paulo Moura',
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version is 1.0,
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date is 2000/4/22,
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parnames is ['X', 'Y'],
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comment is '.',
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source is 'Example adopted from the Francis G. McCabe L&O documentation.']).
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:- op(400, yfx, ~).
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:- public(at/2).
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:- mode(at(-integer, -integer), one).
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:- public(crow_flies/2).
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:- mode(crow_flies(+atom, -integer), one).
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:- public(drive/2).
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:- mode(drive(+atom, -nonvar), zero_or_more).
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:- public(links/1).
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:- mode(links(-list), one).
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:- public(road_distance/2).
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:- mode(road_distance(?atom, ?integer), zero_or_more).
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at(X, Y) :-
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parameter(1, X),
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parameter(2, Y).
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crow_flies(Town, Distance) :-
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::at(X, Y),
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Town::at(U, V),
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U0 is U-X,
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V0 is V-Y,
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Distance is sqrt(U0*U0+V0*V0).
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road_distance(Town, Distance) :-
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::links(Links),
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member((Town, Distance), Links).
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drive(To, Route) :- % plan a road journey
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self(Self),
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plan_drive(Self, To, [], _, Route).
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% go directly
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plan_drive(From, To, _, Distance, From~To):-
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To::links(Links),
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member((From, Distance), Links).
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% go indirectly
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plan_drive(From, To, R, D+DI, Route~To):-
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To::links(Links),
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nearest(Links, From, Int, DI),
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\+ member(Int, R),
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plan_drive(From, Int, [To| R], D, Route).
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nearest(Links, To, Int, Distance):-
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quick(metric(To))::sort(Links, Sorted),
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member((Int, Distance), Sorted).
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member(Head, [Head| _]).
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member(Head, [_| Tail]) :-
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member(Head, Tail).
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:- end_object.
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