-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Conal Elliott wrote:
-- Standard instance: applicative functor applied to monoid instance Monoid a => Monoid (IO a) where mempty = pure mempty mappend = (*>)
On second thought, I don't really like (*>), since it's easy to accidentally discard a useful value. (I dislike (>>) for the same reason.)
Exactly; because they don't make monoids, because (x `mappend` mempty) isn't (x), so mempty isn't a right-identity of mappend, so the instance doesn't follow the monoid laws. Isaac -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.6 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iD8DBQFGV2hZHgcxvIWYTTURAjlsAJ0fyUrqYAx09neVi2/FN+sUQobEUACfWAph 2WJwISDe/11pg41lcV80uik= =SYQB -----END PGP SIGNATURE-----