-- Functor:
-- :t (replicate 3)
(replicate 3) :: a -> [a]

-- :t fmap (replicate 3)
(fmap (replicate 3)) :: f a -> f [a]

-- We say that (replicate 3) has been "lifted" to f

-- Also think of functors as things that output values.
-- fmap'ing a functor is attaching a modifier to the output(s) of the functor
-- partial applications of a function are themselves functors
-- fmap'ing these partial applications results in composition!

-- Applicative functors - Applicative class in Haskell
class (Functor f) => Applicative f where
  pure :: a -> f a
  (<*>) :: f (a -> b) -> (f a -> f b)