-- | @delete z@ removes the element at the cursor (if any).
-- Safe to call on an empty zipper.
-- forall x z. delete (insert x z) == z
delete :: Zipper a -> Zipper a
delete (Zip ls (_:rs)) = Zip ls rs
delete :: Zipper a -> Zipper a
delete (Zip ls (_:rs)) = Zip ls rs
delete (Zip ls (_:rs)) = Zip ls rs