/* A link and a list are not the same thing.
   There are things that make sense to keep track of
   for a list that are meaningless for links, such as
   how long is the list, which is its last link.
   So link and list should not be represented by the
   same objects. */

class List
{ protected:

    struct Link
    { thing * data;
      Link * next; 

      Link(thing * a, Link * b = NULL)
      { data = a;
        next = b; }
    };

    Link * first;
    Link * last;    // only add this if adding to the end is needed
    int length;     // only add this if knowing the length is needed

  public:

    List();
    void add_to_end(thing * x);
    void add_to_front(thing * x);
    thing * remove_from_front();    // removing from the end is still nasty
    int how_long(); 
};

List::List()
{ first = NULL;
  last = NULL;
  length = 0; }

void List::add_to_front(thing * x)
{ /* to be seen */
  length += 1; }

void List::add_to_end(thing * x)
{ /* to be seen */
  length += 1; }

thing * List::remove_from_front()
{ if (front == NULL)
    return NULL;
  /* to be seen */
  length -= 1; }

int List::how_long()
{ return length; }