36 lines
912 B
Prolog
36 lines
912 B
Prolog
:- module(pairs, [pairs_keys_values/3,
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pairs_keys/2,
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pairs_values/2,
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group_pairs_by_key/2,
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map_list_to_pairs/3]).
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:- meta_predicate map_list_to_pairs(0, ?, ?).
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pairs_keys_values([], [], []).
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pairs_keys_values([A-B|ABs], [A|As], [B|Bs]) :-
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pairs_keys_values(ABs, As, Bs).
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pairs_keys(Ps, Ks) :- pairs_keys_values(Ps, Ks, _).
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pairs_values(Ps, Vs) :- pairs_keys_values(Ps, _, Vs).
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map_list_to_pairs(Pred, Ls, Ps) :-
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map_list_to_pairs2(Ls, Pred, Ps).
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map_list_to_pairs2([], _, []).
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map_list_to_pairs2([H|T0], Pred, [K-H|T]) :-
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call(Pred, H, K),
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map_list_to_pairs2(T0, Pred, T).
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group_pairs_by_key([], []).
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group_pairs_by_key([K-V|KVs0], [K-[V|Vs]|KVs]) :-
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same_key(K, KVs0, Vs, KVs1),
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group_pairs_by_key(KVs1, KVs).
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same_key(K0, [K1-V|KVs0], [V|Vs], KVs) :-
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K0 == K1, !,
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same_key(K0, KVs0, Vs, KVs).
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same_key(_, KVs, [], KVs).
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