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     , thread/2
  10     ]).
  11
  12 -spec id(A) ->
  13     A.
  14 id(X) ->
  15     X.
  16
  17 -spec curry(fun()) ->
  18     fun().
  19 curry(F) ->
  20     {arity, Arity} = erlang:fun_info(F, arity),
  21     curry(F, [], Arity).
  22
  23 -spec curry(fun(), list(), integer()) ->
  24     fun().
  25 curry(F, Args, 0) ->
  26     apply(F, lists:reverse(Args));
  27 curry(F, Args, Arity) ->
  28     fun (X) -> curry(F, [X | Args], Arity - 1) end.
  29
  30 -spec compose([fun((A) -> B)]) ->
  31     fun((A) -> B).
  32 compose(Fs) ->
  33     compose_right(Fs).
  34
  35 -spec compose_right([fun((A) -> B)]) ->
  36     fun((A) -> B).
  37 compose_right(Fs) ->
  38     compose_given_fold(Fs, fun lists:foldr/3).
  39
  40 -spec compose_left([fun((A) -> B)]) ->
  41     fun((A) -> B).
  42 compose_left(Fs) ->
  43     compose_given_fold(Fs, fun lists:foldl/3).
  44
  45 -spec thread([fun((A) -> B)], A) ->
  46     B.
  47 thread(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).
  56 compose_given_fold(Fs, Fold) ->
  57     fun (X) -> Fold(fun (F, Y) -> F(Y) end, X, Fs) end.