load "Real";
open TextIO Char String Real

exception StackUnderflow
exception BadOperator of string

val _ = while not (endOfStream stdIn) do
    case foldl
             (fn (w, s) =>
                 let
                     fun f opr = case s of
                                     h1 :: h2 :: t => opr (h2, h1) :: t
                                   | _ => raise StackUnderflow
                  in
                      case w of
                          "+" => f (op +)
                        | "-" => f (op -)
                        | "*" => f (op * )
                        | "/" => f (op /)
                        | _ => case fromString w of
                                   NONE => raise BadOperator w
                                 | SOME(value) => value :: s
                 end)
             nil (tokens isSpace (inputLine stdIn)) of
        h :: _ => print ((toString h) ^ "\n")
      | _ => ()