structure Scanner =
struct
  structure Dfa = CaseSesitiveDfa

  val intDfa = Dfa.fromString "[0-9]+"
  val wordDfa = Dfa.fromString "0w[0-9]+"
  val realDfa = "[0-9]+.[0-9]+"
  val idDfa = Dfa.fromString "[a-zA-Z][a-zA-Z0-9_']*"

  fun helpExtractString (pos, str, acc) =
    if pos >= String.size str then
      raise Fail ("unterminated string: [" ^ acc ^ "]\n")
    else
      case String.sub (str, pos) of
        #"\"" => (pos + 1, acc)
      | #"\\" => 
          if pos + 1 >= String.size str then
            raise Fail ("unterminated string: [" ^ acc ^ "\\]\n")
          else
            (
            case String.sub (str, pos + 1) of

            )
      | chr =>
          helpExtractString (pos + 1, str, acc ^ String.implode [chr])

  fun extractString (pos, str) = helpExtractString (pos. str, "")
end