Reverse Polish notation

#load "str.cma";;

let string_to_tokens = Str.split (Str.regexp " +");;

let push nombre liste = nombre::liste;;

let pop = function
    | [] ->failwith "Pile vide ! "
    | head::tail -> (head,tail);;

let is_operator = function
    |"+"|"-"|"/"|"*" -> true
    | _ -> false

let operator_to_function = function
    | "+" -> ( + )
    | "-" -> ( - )
    | "/" -> ( / )
    | "*" -> ( * )
    | _ -> failwith "Operateur inconnu !";;

let rec parse liste pile =
    match liste with
    | [] -> let (reponse,pilevide) = pop pile in
        reponse
    | token::reste -> Printf.printf "Token:%s \n" token;
              let pilenew = if (is_operator token) then
                let (b,pileun) = pop pile in
                let (a,piledeux) = pop pileun in
                push ((operator_to_function token) a b) piledeux
              else push (int_of_string token) pile in
              parse reste pilenew;;



let () =
  if (Array.length Sys.argv = 2) then
      let arg = Sys.argv.(1) in
      let chaine = string_to_tokens arg in
      try (
      let result = parse chaine [] in
      Printf.printf "\n==> Resultat : %d\n\n" result;
      exit 0
      ) with
        | Failure a -> Printf.printf "[Erreur] %s\n" (if (a="int_of_string") then "conversion en nombre impossible !" else a)
  else exit 1;;