nested.hs

data Nested = Empty | Nest Nested 
  deriving Show

grow :: Int -> Nested
grow 0 = Empty
grow n = Nest (grow $ n - 1)

depth :: Nested -> Int
depth Empty = 0
depth (Nest xs) = 1 + depth xs

demo :: Int -> IO ()
demo = print . grow

main = do demo 1
          demo 10
          demo 100