On Dec 15, 2011, at 10:19 AM, Brent Yorgey wrote: > On Thu, Dec 15, 2011 at 06:49:13PM +1000, Gregory Crosswhite wrote: >> >> So at the end of the day... what is the point of even making Maybe and [] >> instances of Alternative? > > The Alternative and Monoid instances for [] are equivalent. However, > the Alternative and Monoid instances for Maybe are not. To wit: > >> (Just (Sum 4)) <|> (Just (Sum 3)) > Just (Sum {getSum = 4}) > >> (Just (Sum 4)) `mappend` (Just (Sum 3)) > Just (Sum {getSum = 7})
We already have, > First (Just (Sum 4)) `mappend` First (Just (Sum 3)) First {getFirst = Just (Sum {getSum = 4})} So the overlap of apparent Alternative and Monoid functionality remains. This just represents an opportunity for the caller to select the monoid they want. Anthony _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe