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November 12, 2013 16:10
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%% keyfold: extension to stdlib's lists module.
%% Intersection of lists:fold{l,r}/3 and lists:keymap/3.
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%% Copyright © 2013 Pierre Fenoll ‹pierrefenoll@gmail.com› | |
%% See LICENSE for licensing information. | |
%% -*- coding: utf-8 -*- | |
-module(keyfold). | |
%% keyfold: extension to stdlib's lists module. | |
%% Intersection of lists:fold{l,r}/3 and lists:keymap/3. | |
-include_lib("eunit/include/eunit.hrl"). | |
-export([keyfoldl/4]). | |
-export([keyfoldr/4]). | |
%% API | |
keyfoldl (F, A, K, T) -> | |
keyfold(F, A, fun lists:foldl/3, K, T). | |
keyfoldr (F, A, K, T) -> | |
keyfold(F, A, fun lists:foldr/3, K, T). | |
%% Tests | |
keyfoldl_test_ () -> | |
Tuples = [{1,5}, {2,4}, {3,3}, {4,2}, {5,1}], | |
[ ?assertEqual(keyfoldl(fun (X, Acc) -> X + Acc end, 0, 2, Tuples), 15) | |
, ?assertEqual(keyfoldl(fun (X, Acc) -> [X|Acc] end, [], 1, Tuples), | |
[5,4,3,2,1]) ]. | |
keyfoldr_test_ () -> | |
Tuples = [{1,5}, {2,4}, {3,3}, {4,2}, {5,1}], | |
[ ?assertEqual(keyfoldr(fun (X, Acc) -> X * Acc end, 1, 2, Tuples), 120) | |
, ?assertEqual(keyfoldr(fun (X, Acc) -> [X|Acc] end, [], 1, Tuples), | |
[1,2,3,4,5]) ]. | |
%% Internals | |
keyfold (Fun, AccIn, Fold, Key, Tuples) -> | |
Fold(fun (Tuple, Acc) -> | |
Elem = element(Key, Tuple), | |
Fun(Elem, Acc) | |
end, AccIn, Tuples). | |
%% End of Module. |
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