{-# LANGUAGE GADTs #-}

import Data.Coerce
import Data.Ord (Down(..))

data OddPair b where
  OddPair :: forall a b . Coercible a b => a -> b -> OddPair b

foo :: OddPair [Int]
foo = let x = [1, 2, 3] in OddPair (Down x) x
{-# NOINLINE foo #-}

main :: IO ()
main = case foo of
  OddPair x y -> print (coerce x ++ y)