data Triple a = Tr a a a deriving (Eq,Show)

instance Functor Triple where
  fmap f (Tr x y z) = Tr (f x) (f y) (f z)

instance Applicative Triple where
  pure f = Tr f f f
  (<*>) (Tr fx fy fz) (Tr x y z) = (Tr (fx x) (fy y) (fz z))

instance Foldable Triple where
  foldr ff ini (Tr a b c) = ff a (ff b (ff c ini))

instance Traversable Triple where
  --traverse :: (a -> f b) -> t a -> f (t b)
  traverse g (Tr a b c) = Tr <$> g a <*> g b <*> g c