src/hope_option.erl

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