| Ok thanks. It would also be nice to allow forall in instance
| declarations so that the following would be possible.
|
| import ST
|
| class Run s c where
| run :: s c -> c
|
| instance Run (forall s. ST s) c where
| run a = runST a
First of all, the scoping here is wrong. This example is nonsense
because (forall s. ST s) c isn't the same as (forall s. ST s c).
Secondly, this example puts forall's into a completely new context,
and I'm not sure we know how to make unification work when with
such types. That, after all, is why we have to give forall's a
special case treatment to begin with. Much better, it seems to
me, to write:
newtype Runnable a = Runnable (forall s. ST s a)
and then define:
instance Run Runnable a where run (Runnable p) = runST p
I'm not sure you even want a two parameter class for Run here.
Mark
