Is there a Monoid instance defined for IO () anywhere? I'm using the following,

instance Monoid (IO ()) where { mempty = pure mempty; mappend = (*>) }

This definition follows a general form mentioned in http://haskell.org/haskellwiki/TypeComposition,

instance (Applicative f, Monoid a) => Monoid (f a) where
mempty = pure mempty
mappend = (*>)

without the conflicts (overlapping instances) introduced by this definition.

- Conal