10 Apr
2014
10 Apr
'14
2:06 a.m.
On Wed, Apr 9, 2014 at 11:05 AM, Alexander Solla <alex.solla@gmail.com>wrote:
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?