data ZipList a = ZL [a] a [a] deriving (Eq, Show)

test :: ZipList Int
test = ZL [3,2,1] 4 [5,6,7]

-- Create a new empty list and make e the default item that is
newZipList :: a -> ZipList a
newZipList x = ZL [] x []

-- Returns true if only one item present
-- i.e. the left and right lists are empty
isSingleton :: ZipList a -> Bool
isSingleton (ZL [] _ []) = True
isSingleton _            = False

-- Move the current item one place forwards in the list
after :: ZipList a -> ZipList a
after (ZL ls x [])     = ZL ls x [] -- Can't go any further right
after (ZL ls x (r:rs)) = ZL (x:ls) r rs

-- Move the current item one place backwards in the list
before :: ZipList a -> ZipList a
before (ZL [] x rs)     = ZL [] x rs -- Can't go any further left
before (ZL (l:ls) x rs) = ZL ls l (x:rs)