Re: Restricted sums in BoxedRep

Ok, I believe get it now, Let's imagine (to take only the simplest case) that we have a `Nullable# a` type, such that `Nullable# a = (# (##) | a #)`. What would be the kind of `Nullable#`? I imagine that it would be something like `TYPE (BoxedRep Lifted) -> TYPE (BoxedRep Nullable)`. Then you would want to abstract the type of arrays/tvars/whatnot from `Type -> Type` to `forall r. TYPE (BoxRep r) -> Type`. Is that a correct interpretation of your suggestion? If so, my guess would be that all the above is fine, but I suspect (and I'm quite a bit out of my comfort zone here) that there can be considerable difficulties in implementing pattern-matching for such a type.