newtype abstraction problem

[Alastair Reid]

> I can't see a simple solution.  Perhaps we just declare that when a
> newtype is exported abstractly, it's suitability as a foreign argument
> type is still visible.

This feels a little like the global visibility of class instances.
If I export a type T abstractly, all its instances are exported too.
(In that sense, SimonPJ's old CCallable/CReturnable classes were right on the 
money.)

--
Alastair