public void report_error(String message, Object info)
    {
      System.err.print(message);
      System.err.flush();
      if (info instanceof Symbol)
	if (((Symbol)info).left != -1)
	System.err.println(" at character " + ((Symbol)info).left + 
			   " of input");
	else System.err.println("");
      else System.err.println("");
    }