open Random
    open Graphics

    let rec iterate r x_init i =
        if i = 1 then x_init
        else
            let x = iterate r x_init (i - 1) in
            r *. x *. (1.0 -. x)

    let main () =
        self_init ();
        open_graph " 640x480";

        for x = 0 to 639 do
            let r = 4.0 *. (float_of_int x) /. 640.0 in
            for i = 0 to 39 do
                let x_init = Random.float 1.0 in
                let x_final = iterate r x_init 500 in
                let y = int_of_float (x_final *. 480.) in
                Graphics.plot x y
            done
        done;

        ignore (read_line ())

    let () = main ()

https://github.com/ocaml/ocaml.org/tree/master/site/learn/tu...