9 Apr
2014
9 Apr
'14
6:06 p.m.
On Wed, Apr 9, 2014 at 11:05 AM, Alexander Solla
Try using scoped type variables, and explicitly declare the types for pack and unpack at the call site:
instance (Newtype a b, Newtype b c) => Newtype a c where pack = (pack :: b -> c) . (pack :: a -> b)
Did I get those types right? They look free to me.
Actually, I'm not sure if that will work. How will GHC know which b to choose for the pair a and c, unless there are functional dependencies on a and c?