+
+-spec iter(t(A), fun((A) -> (any()))) ->
+ {}.
+iter({some, X}, F) ->
+ _ = F(X),
+ {};
+iter(none, _) ->
+ {}.
+
+-spec pipe([fun((A) -> t(B))], A) ->
+ t(B).
+pipe([], X) ->
+ return(X);
+pipe([F|Fs], X) ->
+ case F(X)
+ of none -> none
+ ; {some, Y} -> pipe(Fs, Y)
+ end.
+
+-spec of_result(hope_result:t(A, _B)) ->
+ t(A).
+of_result({ok, X}) -> {some, X};
+of_result({error, _}) -> none.
+
+-spec of_undefined(undefined | A) ->
+ t(A).
+of_undefined(undefined) -> none;
+of_undefined(X) -> {some, X}.
+
+-spec to_undefined(t(A)) ->
+ undefined | A.
+to_undefined(none) -> undefined;
+to_undefined({some, X}) -> 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.