On Sun, Dec 02, 2007 at 09:57:50AM -0800, Conal Elliott wrote:
My proposed addition:
-- | Ordered monoid under 'max'. newtype Max a = Max { getMax :: a } deriving (Eq, Ord, Read, Show, Bounded)
instance (Ord a, Bounded a) => Monoid (Max a) where mempty = Max minBound Max a `mappend` Max b = Max (a `max` b)
Funny, I was thinking of proposing a Max type that adjoined a synthetic identity, as we did in the finger tree paper: data Max a = NoMax | Max a deriving (Eq, Ord, Read, Show) instance Ord a => Monoid (Max a) where mempty = NoMax NoMax `mappend` b = b a `mappend` NoMax = a Max x `mappend` Max y = Max (x `max` y) and similarly for Min. One could even define getMax :: Bounded a => Max a -> a getMax NoMax = minBound getMax (Max x) = x