クイックソートなり.

quick_sort.ml

let rec partition p = function
  | [] -> [], []
  | hd :: tl ->
     let ll, rl = partition p tl in
     if p hd then
       hd :: ll, rl
     else
       ll, hd :: rl

let rec quick_sort = function
  | [] -> []
  | [x] -> [x]
  | pivot :: rest ->
     let ll, rl = partition (fun x -> x < pivot) rest in
     (quick_sort ll) @ [pivot] @ (quick_sort rl)