Strange.hs

instance Fractional Integer where
    fromRational x = 0
instance Fractional Int where
    fromRational x = 1

a :: Int
a = 0

b :: Fractional a => a
b = 0.0

c :: Int
c = 0

d :: Fractional a => a
d = 0.0


main = do
  print $ a + c == 0 -- True.
  print $ a == c     -- True. a == c == 0.
  print $ c == 0     -- True. Of course.
  print $ a + d == 1 -- True. d == 1.
  print $ b + c == 1 -- True. b == 1.
  print $ b + d == 0 -- True. What happened?!
  print $ b == d     -- True. ?!
  print $ d == 0     -- True. ?!?!
  -- hints to make answer unique (perhaps...)
  print $ sum [a, b, c]   -- 1
  print $ sum [a, b, d]   -- 1
  print $ [a, b, c] !! a  -- 0
  print $ [a, b, c] !! b  -- 1
  print $ [a, b, c] !! c  -- 0