data Bag = String [Bag]

head :: String -> Bag
head s = s []

join :: String -> String -> Bag -> Bag
join p d (x xs) =
    if p /= x && notElem p xs
        then x xs
        else if p == x
                 then x xs:(d [])
                 else x (take elementBag xs):((y (_ zs) -> (_ zs:d)) d xs!!elementBag):(drop elementBag+1 xs)
                     where elementBag = length (takeWhile ((y _) -> y = p) xs)