Question about types

[Wojciech Moczydlowski, Jr]

  I have a question regarding standard. The follow piece of code is accepted
by hugs and ghc, rejected by nhc and (I haven't seen it) by hbc. Is this
code correct or not?

type A = Either Int

f :: (a -> b) -> A a -> A b
f _ _ = Left 0

Wojciech Moczydlowski, Jr