// Example of a polymorphic type using a distinct Node template

#include <iostream.h>
#include <stdlib.h>
#include <ctype.h>


void error(char * m){ cout << m; exit(1);}

class poly;
template <class t> struct node;

class poly {
public: enum Tag { I, P };
private: 
 union { int i; node<poly> * p; };
 Tag tag;
 void check(Tag t){ if (tag!=t) error("bad access");}
public:
 Tag get_tag() { return tag; }
 int & ival() { check(I); return i; }
 node<poly> * & pval() { check(P); return p; }
public:
 // Creating a new poly
 poly() { i=0; tag=I; }
 poly(int ii) { i=ii; tag=I; }
 poly(node<poly> * pp) { p=pp; tag=P; }
 // Changing the value in a poly
 void set(int ii) { i=ii; tag=I; }
 void set(node<poly> * pp) { p=pp; tag=P; }

 void print_preorder(void);

};


template <class t> struct node {
	t data;
	node<t>* next; };


void poly::print_preorder (void)
{ 
  if (get_tag()==I) cout << ival() << " ";
  else { // must be pointer to a node
    node<poly> * np = pval();
    while (np != NULL){
      (np->data).print_preorder();
      np = np->next;
    }
  }
}

int main(){
  poly p1;
  poly p2;
  poly p3;

  p1.set(11);
  
  p1.print_preorder(); cout<<endl;
  p2.set(22);
  p3.set(33);

  node<poly> n2;
  node<poly> n3;
  n2.data.set(22);
  n3.data.set(33);
  n2.next = &n3;
  n3.next = NULL;

  p1.set(&n2);

  p1.print_preorder(); cout<<endl;


  return 0;
}