Elementary Cellular Automaton (http://mathworld.wolfram.com/ElementaryCellularAutomaton.html)

main.ml

let print_row row =
  Array.map print_char row |> ignore;
  print_newline ()


let rule n = function
  | ('_', '_', '_') -> if n land 0b00000001 = 0 then '_' else '*'
  | ('_', '_', '*') -> if n land 0b00000010 = 0 then '_' else '*'
  | ('_', '*', '_') -> if n land 0b00000100 = 0 then '_' else '*'
  | ('_', '*', '*') -> if n land 0b00001000 = 0 then '_' else '*'
  | ('*', '_', '_') -> if n land 0b00010000 = 0 then '_' else '*'
  | ('*', '_', '*') -> if n land 0b00100000 = 0 then '_' else '*'
  | ('*', '*', '_') -> if n land 0b01000000 = 0 then '_' else '*'
  | ('*', '*', '*') -> if n land 0b10000000 = 0 then '_' else '*'
  | _ -> 'E'


let ngen len r g g' =
  for i = 0 to len - 3 do
    let a = rule r (Array.get g  i,
                    Array.get g (i+1),
                    Array.get g (i+2))
    in Array.set g' (i+1) a
  done

let run r gens =
  let len = 43 in
  let g = Array.make len '_' in
  let g' = Array.make len '_' in
  Array.set g (len / 2) '*';
  print_row g;
  for i = 0 to gens do
    if i mod 2 = 0
    then
      (ngen len r g g';
      print_row g')
    else
      (ngen len r g' g;
      print_row g)
  done

let _ =
  if Array.length Sys.argv != 3
  then (
    Printf.printf "Usage: %s <rule #> <# of generations>\n" (Array.get Sys.argv 0);
    exit 1
  )
  else (
    let rule_num = int_of_string (Array.get Sys.argv 1) in
    let num_gens = int_of_string (Array.get Sys.argv 2) in
    run rule_num num_gens
  )