]).
-export(
- [ put/2
- , get/2
- , return/1
+ % Generic monad interface
+ [ return/1
, map/2
- , iter/2
, pipe/2
+
+ % Specific to hope_option:t()
+ , return/2
+ , put/2
+ , get/2
+ , iter/2
, of_result/1
, of_undefined/1
+ , validate/2
]).
-spec put(A, fun((A) -> boolean())) ->
t(A).
put(X, F) ->
- case F(X)
- of true -> {some, X}
- ; false -> none
- end.
+ return(X, F).
-spec get(t(A), Default :: A) ->
A.
return(X) ->
{some, X}.
+-spec return(A, fun((A) -> boolean())) ->
+ t(A).
+return(X, Condition) ->
+ case Condition(X)
+ of true -> {some, X}
+ ; false -> none
+ end.
+
-spec map(t(A), fun((A) -> (B))) ->
t(B).
map({some, X}, F) -> {some, F(X)};
map(none , _) -> none.
--spec iter(t(A), fun((A) -> (ok))) ->
- ok.
-iter({some, X}, F) -> ok = F(X);
-iter(none , _) -> ok.
+-spec iter(t(A), fun((A) -> (any()))) ->
+ {}.
+iter({some, X}, F) ->
+ _ = F(X),
+ {};
+iter(none, _) ->
+ {}.
-spec pipe([fun((A) -> t(B))], A) ->
t(B).
t(A).
of_undefined(undefined) -> none;
of_undefined(X) -> {some, X}.
+
+-spec validate(t(A), fun((A) -> boolean())) ->
+ t(A).
+validate(none, _) ->
+ none;
+validate({some, X}=T, F) ->
+ case F(X)
+ of false -> none
+ ; true -> T
+ end.