Anna meets Cata

Fold.hs

foldr ::
  (a -> b -> b)
  -> b
  -> [a]
  -> b

-- same:

foldr ::
  ((a, b) -> b)
  -> b
  -> [a]
  -> b

-- same:

foldr ::
  ((a, b) -> b, b)
  -> [a]
  -> b

-- same:

foldr ::
  (Maybe (a, b) -> b)
  -> [a]
  -> b

-- reverse the arrows:

unfoldr ::
  (b -> Maybe (a, b))
  -> b
  -> [a]

-- The End