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[hope.git] / src / hope_fun.erl
... / ...
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1-module(hope_fun).
2
3-export(
4 [ id/1
5 , curry/1
6 , compose/1 % alias for compose_right/1
7 , compose_right/1
8 , compose_left/1
9 , thread/2
10 ]).
11
12-spec id(A) ->
13 A.
14id(X) ->
15 X.
16
17-spec curry(fun()) ->
18 fun().
19curry(F) ->
20 {arity, Arity} = erlang:fun_info(F, arity),
21 curry(F, [], Arity).
22
23-spec curry(fun(), list(), integer()) ->
24 fun().
25curry(F, Args, 0) ->
26 apply(F, lists:reverse(Args));
27curry(F, Args, Arity) ->
28 fun (X) -> curry(F, [X | Args], Arity - 1) end.
29
30-spec compose([fun((A) -> B)]) ->
31 fun((A) -> B).
32compose(Fs) ->
33 compose_right(Fs).
34
35-spec compose_right([fun((A) -> B)]) ->
36 fun((A) -> B).
37compose_right(Fs) ->
38 compose_given_fold(Fs, fun lists:foldr/3).
39
40-spec compose_left([fun((A) -> B)]) ->
41 fun((A) -> B).
42compose_left(Fs) ->
43 compose_given_fold(Fs, fun lists:foldl/3).
44
45-spec thread([fun((A) -> B)], A) ->
46 B.
47thread(Fs, X) ->
48 F = compose_left(Fs),
49 F(X).
50
51
52%% ============================================================================
53
54-spec compose_given_fold([fun((A) -> B)], fun((fun((A, B) -> C), B, [A]) -> C)) ->
55 fun((A) -> C).
56compose_given_fold(Fs, Fold) ->
57 fun (X) -> Fold(fun (F, Y) -> F(Y) end, X, Fs) end.
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