On Fri, Jul 26, 2013 at 10:42 PM, Wvv <vitea3v@rambler.ru> wrote:

First useful use is in Typeable.
In GHC 7.8
class Typeable (a::k) where ... <<==>> class Typeable (a ::**) where ...

But we can't write
data Foo (a::k)->(a::k)->* ... deriving Typeable

Why not? This works fine in 7.7, as far as I know.

Cheers,
Pedro