////   This file contains the C++ code from Program 5.11 of//   "Data Structures and Algorithms//    with Object-Oriented Design Patterns in C++"//   by Bruno R. Preiss.////   Copyright (c) 1998 by Bruno R. Preiss, P.Eng.  All rights reserved.////   http://www.pads.uwaterloo.ca/Bruno.Preiss/books/opus4/programs/pgm05_11.cpp//class Visitor{public:    virtual void Visit (Object&) = 0;    virtual bool IsDone () const	{ return false; }};