-- format a 2d array of integers neatly
show2d a =
  unlines
    [ unwords
       [ printf "%3d" (a ! (x, y) :: Integer)
       | x <- axis fst ]
    | y <- axis snd ]
  where
    (l, h) = bounds a
    axis f = [f l .. f h]

main = mapM_ (putStr . ('\n' :) . show2d . zigZag) [(3, 3), (4, 4), (10, 2)]