ZipList.hs

module ZipList where

type ZipList a = ([a], [a])

newList :: ZipList a
newList = ([], [])

moveLeft :: ZipList a -> ZipList a
moveLeft ((a:b), c) = (b, (a:c))
moveLeft _ = error "Invalid operation"

moveRight :: ZipList a -> ZipList a
moveRight (a, (b:c)) = ((b:a), c)
moveRight _ = error "Invalid operation"

insert :: a -> ZipList a -> ZipList a
insert x (a, b) = (a, (x:b))

delete :: ZipList a -> ZipList a
delete (a, (b:c)) = (a, c)
delete _ = error "Invalid operation"

update :: a -> ZipList a -> ZipList a
update x (a, (b:c)) = (a, (x:c))
update _ _ = error "Invalid operation"

get :: ZipList a -> a
get (_, (x:_)) = x
get _ = error "Invalid operation"

rewind :: ZipList a -> ZipList a
rewind ([], c) = ([], c)
rewind ((a:b), c) = rewind (b, (a:c))

index :: ZipList a -> Int
index (a, b) = length a

moveTo :: Int -> ZipList a -> ZipList a
moveTo x z
  | idx == x = z
  | idx > x = moveTo x (moveLeft z)
  | otherwise = moveTo x (moveRight z)
  where
   idx = index z