2012/2/7 Mikhail Vorozhtsov
Ah, sorry, I got sloppy. Have you encountered situations where partial application of such "constraint aliases" becomes a problem?
In the particular case of the Existential class I'm not sure (it's hard to imagine a real-world application for it in the first place), but, in general, yes: the (:&:) combinator from Control.Constraint.Combine depends on it, for example. You want to be able to write: type MyExists = Exists1 (MonadState A :&: MonadWriter B :&: MonadReader C) That's a bad example because monads aren't very useful with existentials, but you get the idea. For ExistentialWith it might not particularly matter, but for client code the class+instance way is all advantage and no drawback, so I see no reason not to prefer it.