src/hope_fun.erl

   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.