Haskell Stacks funktionen

module Stack(Stack,emptyStack,iSE) where
  data Stack a = Leer | Cons a deriving Show

  emptyStack = []

  iSE:: [a]-> Bool
  iSE [] = True
  iSE _ = False

 -- push :: a -> a -> [a]
  push s e= s ++ [e]

  top s = s !! (length s -1)

  pop :: [a] -> [a]
  pop = init

  s= push (push [2.0] 7.0) 3.0

  -- module Stack(Stack,emptyStack,iSE) where
  --    data Stack a = Leer | Cons a (Stack a)

  diev :: Int -> Int -> Int
  diev a b | a < b = 0
           | otherwise = (diev (a - b ) b) +1
  add :: [Float]->[Float]
  add s | length s > 2 = push (pop (pop s)) ((s !! ((length s) - 2)) + (s !! ((length s) -1)))
        | length s == 2 = push emptyStack ((s !! ((length s) - 2)) + (s !! ((length s) -1)))
        | otherwise = error"2249"

  sub :: [Float]->[Float]
  sub s | length s > 2 = push (pop (pop s)) ((s !! ((length s) - 2)) - (s !! ((length s) -1)))
        | length s == 2 = push emptyStack ((s !! ((length s) - 2)) - (s !! ((length s) -1)))
        | otherwise = error"2253"

  mul :: [Float]->[Float]
  mul s | length s > 2 = push (pop (pop s)) ((s !! ((length s) - 2)) * (s !! ((length s) -1)))
        | length s == 2 = push emptyStack ((s !! ((length s) - 2)) * (s !! ((length s) -1)))
        | otherwise = error"2249"
  pdiv :: [Float]->[Float]
  pdiv s | length s > 2 = push (pop (pop s)) ( (s !! ((length s) - 2)) / (s !! ((length s) -1)))
         | length s == 2 = push emptyStack ( (s !! ((length s) - 2)) / (s !! ((length s) -1)))
         | otherwise = error"2249"
  main :: IO()
  main = print(add (add s))