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     , iter/2
  13     ]).
  14
  15
  16 -type t(A) ::
  17       none
  18     | {some, A}
  19     .
  20
  21
  22 -spec put(A, fun((A) -> boolean())) ->
  23     t(A).
  24 put(X, F) ->
  25     case F(X)
  26     of  true  -> {some, X}
  27     ;   false -> none
  28     end.
  29
  30 -spec get(t(A), Default :: A) ->
  31     A.
  32 get({some, X}, _) -> X;
  33 get(none     , Y) -> Y.
  34
  35 -spec map(t(A), fun((A) -> (B))) ->
  36     t(B).
  37 map({some, X}, F) -> {some, F(X)};
  38 map(none     , _) -> none.
  39
  40 -spec iter(t(A), fun((A) -> (ok))) ->
  41     ok.
  42 iter({some, X}, F) -> ok = F(X);
  43 iter(none     , _) -> ok.