#include <stream.h>
typedef void* ent;

class NonEmptyList {
  friend class repetition;
  friend class repetition_iterator;
  NonEmptyList *next;
  ent e;
  NonEmptyList (ent a, NonEmptyList *p) 
    { e = a; next = p;}
  };

class repetition {
  friend class repetition_iterator;
  NonEmptyList *last;
  public:
  	repetition() { last = 0; }
  	repetition(ent a) { last = new NonEmptyList(a,0);
			    last->next = last; }
       ~repetition() {}
  int   insert(ent a);
  int 	append(ent a);
  ent 	get();
  int	list_length();
  ent	car();
  void	cdr();
  ent	lastexp();
  ent	n_th(int a);
  int 	conc(ent a , ent b);
  int	concatenate(repetition * );
};
  

class repetition_iterator {
  NonEmptyList *ce; //current element
  repetition *cs;   //list
  public:
    repetition_iterator(repetition &s) {cs = &s; ce = cs->last; }
    ent operator()() {
      ent ret = ce ? (ce = ce->next)->e : 0; // Law violation; friend documents
      if (ce == cs->last)
	ce = 0;
      return ret;
    }
};