types.hs

f1 = (<$>  ((:[]) <$>)) 
f1 :: (Functor f) => (f [a] -> b) -> f a  -> b
   :: (Functor f) => (f [a] -> b) -> (f a  -> b)
(=<<) :: (Monad m) => (a -> m b) -> m a -> m b
      :: (Monad m) => (a -> m b) -> (m a -> m b)
-- Applying f1 to (=<<)
f = f1 (=<<) 
f :: (a -> b) -> [a] -> [b]
  :: (a -> b) -> ([a] -> [b])
  
-- Matching type of `(=<<)` with (f [a] -> b)
f [a] -> b
(e -> [a]) -> b -- as f ~ (e ->)

(a -> m b) -> (m a -> m b)
(a -> [b]) -> ([a] -> [b])
(e -> [a]) -> ([e] -> [a])
-- so b ~ ([e] -> [a])