Re: [Haskell-cafe] nested maybes

J. Garrett Morris wrote:

Maybe has a Monad instance, so you can write this as follows (untested):

exists str wmap = boolFromMaybe exists' where exists' = do x <- Map.lookup (sort str) wmap find (== str) (snd x) boolFromMaybe (Just _) = True boolFromMaybe Nothing = False

Small improvement (Data.Maybe is underappreciated):

exists str wmap = isJust exists' where exists' = do x <- Map.lookup (sort str) wmap find (== str) (snd x)

and maybe another improvement, though this is dependent on your tastes:

exists s wmap = isJust $ Map.lookup (sort s) wmap >>= find (== s) . snd

-Udo -- Catproof is an oxymoron, childproof nearly so.