 static void advance()
    throws java.io.IOException
    { next_char = System.in.read(); }

  /* initialize the scanner */
  public static void init()
    throws java.io.IOException
    { advance(); }

  /* recognize and return the next complete token */
  public static Symbol next_token()
    throws java.io.IOException
    {
      for (;;)
        switch (next_char)
	  {
	    case '0': case '1': case '2': case '3': case '4': 
	    case '5': case '6': case '7': case '8': case '9': 
	      /* parse a decima