Random.self_init ()

type cell = Dead | Alive
let cell_to_string = function
    | Alive -> "#"
    | Dead -> "_"

let cell_to_int = function
    | Alive -> 1
    | Dead -> 0

let random_cell = fun _ -> if Random.bool () then Dead else Alive ;;
let random_row = fun _ -> Array.init 10 random_cell ;;

let random_grid () = Array.init 10 random_row ;;
let empty_grid () = Array.init 10 (fun _ -> Array.make 10 Dead) ;;

let grid = ref (random_grid ()) ;;

let show_row row =
    for x = 0 to 9 do
        cell_to_string row.(x) |> print_string
    done;
    print_newline () ;;

let show_grid () =
    for y = 0 to 9 do
        show_row !grid.(y)
    done

let read_cell x y =
    !grid.(y mod 10).(x mod 10) ;;

let neighbors x y =
      (read_cell (x + 9) (y + 9) |> cell_to_int)
    + (read_cell    x    (y + 9) |> cell_to_int)
    + (read_cell (x + 1) (y + 9) |> cell_to_int)
    + (read_cell (x + 9)    y    |> cell_to_int)
    + (read_cell (x + 1)    y    |> cell_to_int)
    + (read_cell (x + 9) (y + 1) |> cell_to_int)
    + (read_cell    x    (y + 1) |> cell_to_int)
    + (read_cell (x + 1) (y + 1) |> cell_to_int)

let next_state x y =
    match read_cell x y, neighbors x y with
        | (Dead, 3) -> Alive
        | (Alive, 2) | (Alive, 3) -> Alive
        | _ -> Dead

let update_grid () =
    let next_grid = empty_grid () in
    for y = 0 to 9 do
        for x = 0 to 9 do
            next_grid.(y).(x) <- next_state x y
        done
    done;
    grid := next_grid ;;

while true do
    show_grid () ;
    print_newline () ;
    update_grid () ;
    let _ = read_line () in () ;
done