import Control.Monad
import Control.Applicative

-- Shows that the Monad constraint on sequence can be weakened.
-- See <The Typeclassopedia>
sequence' :: Applicative m => [m a] -> m [a] 
sequence' ms = foldr liftedCons (pure []) ms
    where
      liftedCons = liftA2 (:)
      --liftedCons m m' = (:) <$> m <*> m'

test = sequence' listOfMs == sequence listOfMs
    where listOfMs :: [Maybe Int]
          listOfMs = [pure 3, pure 4, pure 5]