// From the software distribution accompanying the textbook
// "A Practical Introduction to Data Structures and Algorithm Analysis,
// Third Edition (C++)" by Clifford A. Shaffer.
// Source code Copyright (C) 2007-2011 by Clifford A. Shaffer.


template <typename E> class List { // List ADT
private:
  void operator =(const List&) {}      // Protect assignment
  List(const List&) {}           // Protect copy constructor
public:
  List() {}          // Default constructor
  virtual ~List() {} // Base destructor

  // Clear contents from the list, to make it empty.
  virtual void clear() = 0;

  // Insert an element at the current location.
  // item: The element to be inserted
  virtual void insert(const E& item) = 0;

  // Append an element at the end of the list.
  // item: The element to be appended.
  virtual void append(const E& item) = 0;

  // Remove and return the current element.
  // Return: the element that was removed.
  virtual E remove() = 0;

  // Set the current position to the start of the list
  virtual void moveToStart() = 0;

  // Set the current position to the end of the list
  virtual void moveToEnd() = 0;

  // Move the current position one step left. No change
  // if already at beginning.
  virtual void prev() = 0;

  // Move the current position one step right. No change
  // if already at end.
  virtual void next() = 0;

  // Return: The number of elements in the list.
  virtual int length() const = 0;

  // Return: The position of the current element.
  virtual int currPos() const = 0;

  // Set current position.
  // pos: The position to make current.
  virtual void moveToPos(int pos) = 0;

  // Return: The current element.
  virtual const E& getValue() const = 0;
};