appfunctor.hs

import Control.Applicative

-- class (Functor f) => Applicative f where
--   pure :: a -> f a
--   (<*>) :: f (a -> b) -> f a -> f b
-- instance Appilcative Maybe where
--   pure = Just
--   Nothing <*> _ = Nothing
--   (Just f) <*> something = fmap f something

myAction :: IO String
myAction = (++) <$> getLine <*> getLine

main :: IO ()
main = do
  a <- (++) <$> getLine <*> getLine
  putStrLn $ "The two lines concatenated turn out to be : " ++ a

sequenceA :: (Applicative f) => [f a] -> f [a]
-- sequenceA [] = pure []
-- sequenceA (x:xs) = (:) <$> x <*> sequenceA xs
sequenceA = foldr (liftA2 (:)) (pure [])