import Data.Kind

data Box (c :: Type -> Constraint) = forall a. (c a) => MkBox a

instance Animal (Box Animal) where
  noise (MkBox x) = noise x

class Animal a where
  noise :: a -> String

data Sheep = MkSheep
data Cow = MkCow

instance Animal Sheep where
  noise _ = "baaaaah!"

instance Animal Cow where
  noise _ = "moooooo!"

random_animal :: Double -> Box Animal
random_animal n
  | n < 0.5 = MkBox MkSheep
  | otherwise = MkBox MkCow

main :: IO ()
main = do
  let random_number = 0.234
  let animal = random_animal random_number
  putStrLn (noise animal)