I never know there is a van Laarhoven's representation of Free Monad! What's more, van Laarhoven free monad can be used to implement extensible algebraic effects (see https://hackage.haskell.org/package/free-vl). Isn't that awesome?

newtype VLMonad ops a = VLMonad { runVLMonad :: forall m. Monad m => ops m -> m a }

instance Monad (VLMonad ops) where
  return a = VLMonad (\_ -> return a)
  m >>= f = VLMonad (\ops -> runVLMonad m ops >>= f' ops)
   where
    f' ops a = runVLMonad (f a) ops