> The Haskell report explicitly allows recursive newtype definitions.
> So why is it reasonable for a compiler to reject them?
nhc98 rejects circular newtypes which are semantically bottom, like
newtype Void = Void Void
newtype A = A B
newtype B = B A
because it cannot find a representation for them.
nhc98 accepts recursive newtypes which have semantic content, like
newtype Inftype b = A (b,Inftype b)
newtype Alist a = B (Either () (a,Alist a))
because it can find a representation for them.
What is unreasonable about that?
> But I think the issue here is conformance, and I think it is
> clear that nhc98 does not conform to the specification in the
> Haskell 98 Report.
Well, I'm not sure that the specification is entirely clear on this
point. It states that a newtype uses the same representation as the
type it renames. nhc98 claims that if there is no representation for
the type, it can't continue.
Regards,
Malcolm
