/* Polymorphic linked lists - first version */

using System;
using poly;

public class cell
{
 private number head;  // can't use 'object' - too general!
 private cell tail;
 public number CAR { get { return head; } }
 public cell CDR   { get { return tail; } }
 public cell(number h, cell t) {head=h; tail=t;}
 public int length()   // internal visitor
  { int ax = 0;  // accumulator
    for (cell i=this;i!=null;i=i.tail) ax++;
    return ax;
  }
 public void print()
  {
    Console.Write(head + " ");
    if (tail==null) Console.Write("\n");
      else tail.print();
  }
}

public class polylist
{
  public static int length(cell l) // external visitor
  { 
    if (l==null) return 0; 
      else return 1+length(l.CDR);
  }

  public static void Main()
  { integer n1 = new integer(3);
    rational r1 = new rational(1,2);
    cell l = new cell(n1,new cell(r1,null));
    l.print();
    for(cell m=l;m!=null;m=m.CDR) m.CAR.inc();
    l.print();
  }
}

//complie with csc /r:number.dll polylist.cs