The following datatype declaration would, if possible,
actually be very useful for an application I have in mind:
module Test(V(..)) where
import ST
data V s = forall a . MkV (STRef s a) deriving Eq
Weird! You could never use the reference for anything, because
its type is
The correct behaviour would be to let the above pattern match fail
in the case of different types at r1 and r2,
because the left-hand side has to have a typing
with equal types for r1 and r2
induced by the right-hand side ``r1 == r2''.
But now you are assuming that there is an intentional
