Existential

some.hs

{-# LANGUAGE GADTs #-}

import Data.Some

data ZeroOneTwo a where
    Zero :: ZeroOneTwo ()
    One :: Int -> ZeroOneTwo Int
    Two :: (Int,Int) -> ZeroOneTwo Int

getSome :: Some ZeroOneTwo
getSome = This $ Two (3,10)

useSome :: Some ZeroOneTwo -> Int
useSome (This Zero) = 5
useSome (This (One (x))) = 6
useSome (This (Two (x,y))) = x+y

main = do
    let c = getSome
    let d = useSome c
    print d