[Haskell-cafe] Reflection functional dependency as an associated type?

[Brandon Moore]

I was trying to make a bridge like this
class MonadStateTF m where   type StateOf m :: *instance (MonadState s m) => MonadStateTF m where  type StateOF m = s

to allow writing constraints on state monads without a dangling type parameter
type NumMonad m = (MonadStateTF m, Num (StateOf m))

Unfortunately, the declaration type StateOF m = s
complains that "s" isn't mentioned on the left hand side rather
than somehow making use of the fundep.

Brandon
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