Hi
Indeed, we intend to box everything. Plus there were compilers which did unboxing before having unboxed types - as the paper said, it wasn't as neat, but it was possible.
Right, but the problem is that if you box all of GHC's unboxed types, you end up with an extra layer of boxing compared to an implementation that just boxes everything. ie. it'll be worse than YHC is currently, so you'll need extra trickery to get back to where YHC is now.
Possible, I'll have to think about this further. I was thinking along the lines of newtype Box a = Box !a then Int# = Box Int but I'm not sure if that will work or not. Anyway, its only a question of efficiency, and Yhc has a lot more things that will destroy efficiency than this!
Presumably you lose one bit of precision though, so GHC's Int# type would be 31 bits. We did at one stage have a GHC->OCaml translator with a 31-bit Int#, so it might be possible, but I think there will be some assumptions in the libraries that break (eg. Int32 will need to be implemented using Int64#).
We loose 2 bits, to leave room for enough tag bits. Fortunately this still fills the Haskell specification. We will have some method for implementing Int32, probably as a pointer once again. Thanks Neil