{-# 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
foo n
  | even n = E (show n) id
  | otherwise = E n show

bar' :: Int -> String
bar' n
  | E x1 f1 <- foo n
  , E x2 f2 <- foo (n+1)
  = f1 x1 ++ f2 x2

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