44 lines
1.1 KiB
Plaintext
44 lines
1.1 KiB
Plaintext
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:- object(walker).
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:- info([
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version is 1.0,
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date is 2004/4/29,
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author is 'Paulo Moura',
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comment is 'Walker movements.']).
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:- public(walk/2).
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:- mode(walk(@list, -position), one).
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:- info(walk/2, [
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comment is 'Parses a sequence of walker moves, returning ending position.',
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argnames is ['Moves', 'Ending']]).
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walk(Moves, Ending) :-
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phrase(walk(Ending), Moves).
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walk(Ending) -->
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moves((0, 0), Ending).
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moves(Start, Ending) -->
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move(Start, Temp), moves(Temp, Ending).
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moves(Ending, Ending) -->
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[].
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move((X0, Y0), (X, Y)) --> [ n(S)], {X is X0, Y is Y0 + S}.
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move((X0, Y0), (X, Y)) --> [ne(S)], {X is X0 + S / sqrt(2), Y is Y0 + S / sqrt(2)}.
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move((X0, Y0), (X, Y)) --> [ e(S)], {X is X0 + S, Y = Y0}.
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move((X0, Y0), (X, Y)) --> [se(S)], {X is X0 + S / sqrt(2), Y is Y0 - S / sqrt(2)}.
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move((X0, Y0), (X, Y)) --> [ s(S)], {X is X0, Y is Y0 - S}.
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move((X0, Y0), (X, Y)) --> [sw(S)], {X is X0 - S / sqrt(2), Y is Y0 - S / sqrt(2)}.
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move((X0, Y0), (X, Y)) --> [ w(S)], {X is X0 - S, Y = Y0}.
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move((X0, Y0), (X, Y)) --> [nw(S)], {X is X0 - S / sqrt(2), Y is Y0 + S / sqrt(2)}.
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:- end_object.
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