{-# LANGUAGE ExistentialQuantification #-} module Main where import T7797a data Box = forall a. (Size a) => Box a a box = Box (go 10000000) (go 10000000) where go :: Int -> [Int] go 0 = [] go n = 1 : go (n - 1) {-# NOINLINE box #-} main = print $ case box of Box l r -> size l r