src/hope_option.erl

   1 -module(hope_option).
   2
   3 -export_type(
   4     [ t/1
   5     ]).
   6
   7 -export(
   8     [ put/2
   9     , get/2
  10     , map/2
  11     ]).
  12
  13
  14 -type t(A) ::
  15       none
  16     | {some, A}
  17     .
  18
  19
  20 put(X, F) ->
  21     case F(X)
  22     of  true  -> {some, X}
  23     ;   false -> none
  24     end.
  25
  26
  27 get({some, X}, _) -> X;
  28 get(none     , Y) -> Y.
  29
  30
  31 map({some, X}, F) -> {some, F(X)};
  32 map(none     , _) -> none.