src/hope_option.erl

   1 -module(hope_option).
   2
   3
   4 -export_type(
   5     [ t/1
   6     ]).
   7
   8 -export(
   9     [ put/2
  10     , get/2
  11     , map/2
  12     ]).
  13
  14
  15 -type t(A) ::
  16       none
  17     | {some, A}
  18     .
  19
  20
  21 -spec put(A, fun((A) -> boolean())) ->
  22     t(A).
  23 put(X, F) ->
  24     case F(X)
  25     of  true  -> {some, X}
  26     ;   false -> none
  27     end.
  28
  29 -spec get(t(A), Default :: A) ->
  30     A.
  31 get({some, X}, _) -> X;
  32 get(none     , Y) -> Y.
  33
  34 -spec map(t(A), fun((A) -> (B))) ->
  35     t(B).
  36 map({some, X}, F) -> {some, F(X)};
  37 map(none     , _) -> none.