#ifndef SEQ_H_
#define SEQ_H_ 1

// Code from ftp://ftp.aw.com/cp/koenig/code.tar.Z
// in conjunction with the book \emph{Ruminations on C++}.
/* ***********************************************

Copyright, 1997 AT&T Corporation.  All rights
reserved.  Permission is granted for individuals
to use this material for educational purposes
in connection with the book Ruminations on C++,
Addison-Wesley, 1997, ISBN 0-201-42339-1.

************************************************** */



// added by Oldham 2000Jan15; fixes the friend-template problem.
// Apparently, the C++ standard changed since Stroustrup's third edition.
template <class T> class Seq;
template <class T> int operator==(const Seq<T>&, const Seq<T>&);

template <class T> class Seq_item {
  friend class Seq<T>;
  int use;
  const T data;
  Seq_item* next;
  Seq_item(const T& t, Seq_item* s);
  Seq_item(const T& t): use(1), data(t), next(0) { }
};

template<class T> class Seq {
  friend int operator==<>(const Seq<T>&, const Seq<T>&);
public:
  Seq(): item(0), len(0) { }
  Seq(const T& t, const Seq& x): item(new Seq_item<T>(t, x.item)), len(x.len+1)
 { }
  Seq(const Seq& s): item(s.item), len(s.len) { if (item) item->use++; }
  Seq(Seq_item<T>* s, unsigned l): item(s), len(l) { if (s) s->use++; }

  ~Seq() { destroy(item); }

  Seq& operator=(const Seq&);   
  T hd() const;
  Seq tl() const;
  //operator int() const { return item != 0; }
  operator bool() const { return item; }
  bool empty(void) const { return !item; } // added by Oldham 2000Jan15
  void destroy(Seq_item<T>*);
  Seq<T>& operator++();
  Seq<T>  operator++(int);
  T operator*() { return hd(); }
  Seq<T>& insert(const T&);
  Seq_item<T>* owntail();
  Seq<T>& flip();
  unsigned length() const { return len; } // added by Oldham 2000Feb16
private:
  Seq_item<T>* item;            
  unsigned len;
};

template<class T> Seq<T> cons(const T& t, const Seq<T>& s);

#include "seq.cpp"              // added by Oldham 2000Jan15

#endif // SEQ_H_