DData modules

[Malcolm Wallace]

Ross Paterson <ross at soi.city.ac.uk> writes:

> Also, these modules import Data.Monoid, which contains the non-H98 instance
> Monoid (a -> a), making it (and these) non-portable.

In what sense is
    instance Monoid (a -> a)
not Haskell'98?  It looks perfectly OK to me.  Is it because the two
type variable arguments to (->) are the same?

Regards,
    Malcolm