weak_transpose.hs

transpose :: [[a]] -> [a] -> [a]
transpose [] output = output
transpose input output = transpose
  (filter (\x -> not (null x)) (map (\x -> tail x) input))
  (output ++ (map (\x -> head x) input))

print (transpose [[1, 2, 3], [4, 5], [6, 7, 8]] [])
-- prints [1, 4, 6, 2, 5, 7, 3, 8]