tried some polynomials 1, Haskell

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{-# LANGUAGE InstanceSigs #-}
-- {-# LANGUAGE DatatypeContexts #-}

main :: IO ()
main = do
    print $ foldr (\x acc -> x * acc) 1 Null
    print $ foldr (\x acc -> x * acc) 1 (2:+:Null)
    print $ 1 :+: 2 :+: 3 :+: 4 :+: Null

infixr 5 :+:
data Polynomial a =  Null | a :+: Polynomial a
    deriving (Show, Eq)
    
deg :: (Num a, Eq a) => Polynomial a -> Int
deg Null = -1
deg (c :+: cs) = deg cs + 1

instance Foldable Polynomial where
    --foldr :: (Num a) => (a -> b -> b) -> b -> Polynomial a -> b
    foldr f z Null = z
    foldr f z (c :+: cs) = f c (foldr f z cs)

instance (Num a, Eq a) => Num (Polynomial a) where
    (+) Null g = g
    (+) h Null = h
    (+) h@(a :+: as) g@(b :+: bs)
        | deg h == deg g = a + b :+: as + bs
        | deg h > deg g = a :+: as + g
        | otherwise = b :+: h + bs
    
    (*) Null g = Null
    (*) f Null = Null
    (*) f (b :+: Null) = foldr (\x acc -> (b * x) :+: acc) Null f 
 --   (*) f@(a :+: as) g@(b :+: bs) =
   --     foldl (\x acc -> (a * x) :+: acc)  Polinomial a (deg f)
    
    negate Null = Null
    negate (c :+: cs) = negate c :+: negate cs
    
    abs Null = Null
    abs (c :+: cs) = abs c :+: abs cs
    
    signum = undefined
    
    fromInteger 0 = Null
    fromInteger i = fromInteger i :+: Null
    
toInteger Null = 0
toInteger (c :+: Null) = c
toInteger g = undefined
    
----------

data GF2 = Zero | One
    deriving (Show)
    
instance Num (GF2) where
    (+) Zero Zero = Zero
    (+) Zero One = One
    (+) One Zero = One
    (+) One One = Zero
    
    (*) Zero Zero = Zero
    (*) Zero One = Zero
    (*) One Zero = Zero
    (*) One One = One
    
    (-) Zero Zero = Zero
    (-) Zero One = One
    (-) One Zero = One
    (-) One One = Zero
    
    abs = id
    signum = id
    
    fromInteger k
        | odd k = One
        | otherwise = Zero

--data GF n = 0,1..n
  --  deriving (Show, Num)

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Compilation time: 0.83 sec, absolute running time: 0.24 sec, cpu time: 0.17 sec, memory peak: 3 Mb, absolute service time: 1,08 sec