| 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 | ]). |
| 10 | |
| 11 | -spec id(A) -> |
| 12 | A. |
| 13 | id(X) -> |
| 14 | X. |
| 15 | |
| 16 | -spec curry(fun()) -> |
| 17 | fun(). |
| 18 | curry(F) -> |
| 19 | {arity, Arity} = erlang:fun_info(F, arity), |
| 20 | curry(F, [], Arity). |
| 21 | |
| 22 | -spec curry(fun(), list(), integer()) -> |
| 23 | fun(). |
| 24 | curry(F, Args, 0) -> |
| 25 | apply(F, lists:reverse(Args)); |
| 26 | curry(F, Args, Arity) -> |
| 27 | fun (X) -> curry(F, [X | Args], Arity - 1) end. |
| 28 | |
| 29 | -spec compose([fun((A) -> B)]) -> |
| 30 | fun((A) -> B). |
| 31 | compose(Fs) -> |
| 32 | compose_right(Fs). |
| 33 | |
| 34 | -spec compose_right([fun((A) -> B)]) -> |
| 35 | fun((A) -> B). |
| 36 | compose_right(Fs) -> |
| 37 | compose_given_fold(Fs, fun lists:foldr/3). |
| 38 | |
| 39 | -spec compose_left([fun((A) -> B)]) -> |
| 40 | fun((A) -> B). |
| 41 | compose_left(Fs) -> |
| 42 | compose_given_fold(Fs, fun lists:foldl/3). |
| 43 | |
| 44 | |
| 45 | %% ============================================================================ |
| 46 | |
| 47 | -spec compose_given_fold([fun((A) -> B)], fun((fun((A, B) -> C), B, [A]) -> C)) -> |
| 48 | fun((A) -> C). |
| 49 | compose_given_fold(Fs, Fold) -> |
| 50 | fun (X) -> Fold(fun (F, Y) -> F(Y) end, X, Fs) end. |