[Haskell-cafe] nested maybes

[Martin DeMello]

I have a Data.Map.Map String -> (Layout, [String]) as follows:

type Anagrams = [String]
type Cell = (Layout, Anagrams)
type WordMap = Map.Map String Cell

exists str wmap =
  let a = Map.lookup (sort str) wmap in
      case a of
           Nothing -> False
           Just x -> case (find (== str) (snd x)) of
                          Nothing -> False
                          _       -> True

the existence test looks ugly - any more compact way to write it?

martin