// lists.cpp

#include <iostream>
#include <string>
#include "utility.h"
#include "lists.h"

using namespace std;

link::link(useful * u, link * n)
{ data = u;
  next = n; }

list::list()
{ first = NULL; }

list::~list()
{ while (first != NULL)
  { link * n = first->next;
    delete first;
    first = n; } }

void list::push(useful * u)
{ first = new link(u, first); }

useful * list::pop()
{ if (first == NULL)
    return NULL;
  useful * u = first->data;
  link * n = first->next;
  delete first;
  first = n;
  return u; }

void list::print(ostream & out) const
{ if (first == NULL)
  { out << "[]";
    return; }
  out << "[" << * first->data;
  link * p = first->next;
  while (p != NULL)
  { out << ", " << * p->data;
    p = p->next; }
  out << "]"; }

ostream & operator<<(ostream & out, const list & l)
{ l.print(out);
  return out; }