repro2.hs

data PosInf a = Infinity | Finite a deriving (Show, Read, Eq)

instance Ord a => Ord (PosInf a) where
  compare Infinity Infinity = EQ
  compare Infinity Finite{} = GT
  compare Finite{} Infinity = LT
  compare (Finite a) (Finite b) = compare a b

instance Num a => Num (PosInf a) where
  Finite x + Finite y = Finite (x + y)
  _ + _ = Infinity

some_constant = 3

give_it_a_try :: (Num a, Eq a) => PosInf a -> PosInf a -> PosInf a
give_it_a_try a b
  | a == Infinity || b == Infinity = Infinity
  | otherwise = a + b + Finite some_constant