What kind of problems could crop up if I try to create type variables with an unlifted kind inside GHC (not in user code, just inside the compiler)? I want to make ByteArray# and MutableByteArray# parameterized over their element types. ByteArray# would have kind # -> #, and MutableByteArray#, * -> # -> # . indexByteArray# would have the type (in pseudo haskell) forall (e::#). ByteArray# e -> Int# -> e. This would put all the ByteArray# operations (along with tagToEnum#) in that weird class of primops that have a polymorphic type but must be instantiated with a monomorphic type by the time it hits the code generator but that shouldn't be a big deal. Don't get too hung up on the ByteArray# example. I'm not actually proposing we change ByteArray# (I know it'll cause a few problems with the current UArray implementation). I'm just wondering if something like this is possible, and if so, what I should watch out for if I try to do it. Thanks, -Brian