[Yhc] instance Monad IO bug

[Neil Mitchell]

Hi

> In my version of Yhc it works as expected (same as Hugs and
> GHC).
>
> I haven't done a darcs pull for a week or so; perhaps my
> version is older than yours?

In the last week Tom has committed imprecise exceptions, so Yhc can
now raise an error properly, which nhc can't. Tom also tweaked the >>
and >>= instances and the definition of IO to remove the Either
IOError case from the IO Monad. Obviously something has gone wrong,
we'll look into it.

Dons: I doubt this has anything to do with the slowdown on nobench,
unless the regression has happened in the last week.

Thanks

Neil