On Sun, Dec 4, 2011 at 3:53 AM, Scott Lawrence
type AList = [Event] type BList = [Event] type CList = [Event]
myMapish :: AList -> AList mySelect :: AList -> (Event -> Bool) -> BList myOtherSelect :: BList -> CList
A suggestion: data Exists f = forall a. Exists f a data List a = List [Event] -- your list type myMapish :: List a -> List a myDoSomething :: List a -> (List a, List a) myPair :: (Event -> Event -> Event) -> List a -> List a -> List a mySelect :: List a -> Exists List So the "anonymous, unique type" would be enclosed on the existential. Its real type doesn't really matter, it may be always (), but code that uses mySelect can't use this fact. It's not able to do even something simple like let Exists b = mySelect a Exists c = mySelect a in myPair f b c even though we know that in this case this is valid =). But you can always make unsafeCastList :: List a -> List b unsafeCastList (List a) = List a Cheers, -- Felipe.