src/hope_option.erl

   1 -module(hope_option).
   2
   3 -behavior(hope_monad).
   4
   5 -export_type(
   6     [ t/1
   7     ]).
   8
   9 -export(
  10     [ put/2
  11     , get/2
  12     , return/1
  13     , map/2
  14     , iter/2
  15     , pipe/2
  16     , of_result/1
  17     ]).
  18
  19
  20 -type t(A) ::
  21       none
  22     | {some, A}
  23     .
  24
  25
  26 -spec put(A, fun((A) -> boolean())) ->
  27     t(A).
  28 put(X, F) ->
  29     case F(X)
  30     of  true  -> {some, X}
  31     ;   false -> none
  32     end.
  33
  34 -spec get(t(A), Default :: A) ->
  35     A.
  36 get({some, X}, _) -> X;
  37 get(none     , Y) -> Y.
  38
  39 -spec return(A) ->
  40     {some, A}.
  41 return(X) ->
  42     {some, X}.
  43
  44 -spec map(t(A), fun((A) -> (B))) ->
  45     t(B).
  46 map({some, X}, F) -> {some, F(X)};
  47 map(none     , _) -> none.
  48
  49 -spec iter(t(A), fun((A) -> (ok))) ->
  50     ok.
  51 iter({some, X}, F) -> ok = F(X);
  52 iter(none     , _) -> ok.
  53
  54 -spec pipe([fun((A) -> t(B))], A) ->
  55     t(B).
  56 pipe([], X) ->
  57     return(X);
  58 pipe([F|Fs], X) ->
  59     case F(X)
  60     of  none      -> none
  61     ;   {some, Y} -> pipe(Fs, Y)
  62     end.
  63
  64 -spec of_result(hope_result:t(A, _B)) ->
  65     t(A).
  66 of_result({ok, X})    -> {some, X};
  67 of_result({error, _}) -> none.