haskell merge sort

merge-sort.hs

arr = [x*97 `mod` 61 - 30 | x <- [1..20]]

-- expecting rhs and lhs to be sorted
merge :: Ord a => [a] -> [a] -> [a] -> [a]
merge lhs rhs sorted =
  if length lhs == 0 && length rhs == 0 then
    sorted
  else if length lhs == 0 || (length rhs > 0) && head rhs < head lhs then
    merge (tail rhs) lhs (sorted ++ [head rhs])
  else
    merge rhs (tail lhs) (sorted ++ [head lhs])

sort :: Ord a => [a] -> [a]
sort ls =
  if length ls == 1 then
    ls
  else
    merge (sort (drop n ls)) (sort (take n ls)) []
    where n = (length ls) `div` 2

main :: IO ()
main = putStrLn (show (sort arr))