{-# language BlockArguments #-}

import Data.Functor.Identity

-- This is the worst of both worlds for LOL. Don't do this. :)

data E = forall a. E a (a -> String)

foo :: Int -> (E -> r) -> r
foo n k
  | even n = k (E (show n) id)
  | otherwise = k (E n show)

bar' :: Int -> String
bar' n = runIdentity do
  E x1 f1 <- foo n Identity
  E x2 f2 <- foo (n+1) Identity
  pure (f1 x1 ++ f2 x2)

main :: IO ()
main = putStrLn (bar' 42)