OCAML尾部递归合并排序

let rec merge_sort lst =
  let rec merge l1 l2 =
    match (l1, l2) with
    | ([], _) -> l2
    | (_, []) -> l1
    | (h1 :: t1, h2 :: t2) ->
        if h1 < h2 then h1 :: merge t1 l2 else h2 :: merge l1 t2
  in
  let rec split lst =
    match lst with
    | [] -> ([], [])
    | [x] -> ([x], [])
    | h1 :: h2 :: t ->
        let (left, right) = split t in
        (h1 :: left, h2 :: right)
  in
  let rec tail_merge_sort lst =
    match lst with
    | [] -> []
    | [x] -> [x]
    | _ ->
        let (left, right) = split lst in
        merge (tail_merge_sort left) (tail_merge_sort right)
  in
  tail_merge_sort lst

let () =
  let unsorted_list = [3; 1; 4; 1; 5; 9; 2; 6; 5; 3; 5] in
  let sorted_list = merge_sort unsorted_list in
  print_endline (String.concat " " (List.map string_of_int sorted_list))