let rec length l =
  match l with
    [] -> 0
  | _ :: tl -> 1 + length tl

let rec make_list e k =
  if k = 0 then
    []
  else
    e :: make_list e (pred k)

let rec find_if pred l =
  match l with
    [] -> None
  | e :: t -> if pred e then Some e
              else find_if pred t

let iota n = List.init n (fun x -> x)
           
let time f =
  let start = Sys.time () in
  let _ = f () in
  Sys.time () -. start