halve (xs) | length xs `mod` 2 == 0   = (take n xs, drop n xs)
           | otherwise = (take (n+1) xs,  drop (n+1) xs)
  where n= length xs `div` 2 


main = do
  putStrLn $ show $ halve [1,2,3,4]
  putStrLn $ show $ halve [1,2,3]

([1,2],[3,4])
([1,2],[3])