hspara :: (a -> ([a], b) -> b) -> b -> [a] -> b
para f z [] = z
para f z (x:xs) = f x (xs, para f z xs)hspara :: (a -> ([a], b) -> b) -> b -> [a] -> b
cata :: (a -> b -> b) -> b -> [a] -> b
para f z [] = z
cata f z [] = z
para f z (x:xs) = f x (xs, para f z xs)
cata f z (x:xs) = f x (cata f z xs) (xs, .. の部分で元のobject xs も保存している箇所だけが異なる