Maybe is an instance of Monad; the second signature is just more general than the first. class Monad m where return :: a -> m a (>>=) :: m a -> (a -> m b) -> m b fail :: String -> m a Map lookup only uses "return" and "fail"; for Maybe these are defined as follows: return x = Just x fail s = Nothing So it's really the same thing. -- ryan On Mon, May 11, 2009 at 8:37 AM, Nico Rolle wrote:

Hi everyone.

The docs in the web on http://www.haskell.org/ghc/docs define Data.Map.lookup as follows: http://www.haskell.org/ghc/docs lookup :: Ord k => k -> Map k a -> Maybe a but my version of ghci does i like that: Data.Map.lookup :: (Ord k, Monad m) => k -> Data.Map.Map k a -> m a but i need the 1. one. my version of ghci is 6.8.2 regards _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe