Rule 110 in OCaml

rule110.ml

open List;;

(*
 * Copyright (C) 2023  Gabriel de Brito
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 *)

type cell = I | O;;

let rule110 a b c =
  match (a, b, c) with
  | (I, I, I) -> O
  | (I, I, O) -> I
  | (I, O, I) -> I
  | (I, O, O) -> O
  | (O, I, I) -> I
  | (O, I, O) -> I
  | (O, O, I) -> I
  | (O, O, O) -> O;;

let rec apply_rule110' a l =
  match (a, l) with
  | (x, []) -> [x]
  | (x, [y]) -> [rule110 x y O]
  | (x, y :: r) -> rule110 x y (hd r) :: apply_rule110' y r;;

let apply_rule110 l = apply_rule110' O l;;

(* type handling *)

let print_cell = function
  | I -> print_string "1"
  | O -> print_string " ";;
let rec print_cells = function
  | [] -> print_newline ()
  | c :: r -> print_cell c; print_cells r;;

let rec cell_of_char = function
  | '1' -> I
  | '0' -> O
  | c -> O;; (* unecessary as we garantee the strings to be just 0 and 1 *)

let rec cells_of_char_list = function
  | [] -> []
  | c :: r -> cell_of_char c :: cells_of_char_list r;;

let list_of_string s = init (String.length s) (String.get s);;

let cells_of_string s = cells_of_char_list @@ list_of_string s;;

let rec is_binary' = function
  | [] -> true
  | '1' :: r
    | '0' :: r -> is_binary' r
  | a :: r -> false;;

let is_binary s = is_binary' @@ list_of_string s;;

(* now the program starts to look ugly *)

let rec get_binary prompt =
  print_string prompt;
  let s = read_line () in
  if is_binary s then s else get_binary "Only enter 0s and 1s!: ";;

let get_int prompt =
  print_string prompt;
  int_of_string @@ read_line ();;

let main_loop =
  let n = get_int "Enter number of iterations: " in
  let s = ref @@ cells_of_string @@ get_binary "Enter the initial state: " in
  for i = 1 to n do
    s := apply_rule110 !s;
    print_cells !s;
  done