{-# Language MultiParamTypeClasses, FlexibleContexts, FlexibleInstances, IncoherentInstances, TypeFamilies, PatternGuards, FunctionalDependencies #-}

import Control.Monad

class MonadConcat m a b

    where monadConcat :: a -> m b

instance (Monad m, MonadConcat m (m a) b) => MonadConcat m (m (m a)) b

    where monadConcat x = x >>= monadConcat

instance (Monad m, a ~ b) => MonadConcat m (m a) b

    where monadConcat = id


main = do print $ monadConcat [[[123]],[[345]],[[222],[3333,5555]]]
          print $ monadConcat [2345]
          
          print $ monadConcat (Just 123)
          print $ monadConcat (Just $ Just 345)