/* polymorphic linked lists with a mixture of generics and inheritance */
using System;

// want: linked list with both natural and ad-hoc polymorphic functions

public interface addable<T>
{
   T add(T other);
}

public class integer : addable<integer>
{
   internal int x; // internal means public within same assembly
   public integer(int y) {x=y;} // constructor
   public integer add(integer other) { return new integer(other.x+x); }
   public override string ToString() { return ""+x; }
}

public class rational : addable<rational>
{
   internal int n, d;  // numerator and denominator
   public rational(int a, int b) { n=a;  d=b; }
   public rational add(rational R)
   {  int sd = R.d * d;
      int sn = n*R.d + R.n*d;
      return new rational(sn,sd);
   }
   public override string ToString() { return n+"/"+d; }
}


// polymorphic linked list class
public class cell<T> where T : addable<T>
{
  internal T car;
  internal cell<T> cdr;
  public cell(T a, cell<T> b) {car=a;  cdr=b;} // constructor

  // naturally polymorphic function:
  public int length()
  { int ax = 0; 
    for(cell<T> i=this; i!=null; i=i.cdr) ax++;
    return ax;
  }
  
  // ad-hoc polymorphic function
  public T sum()
  {
     T ax = car;
     for(cell<T> i=cdr; i!=null; i=i.cdr) ax = ax.add(i.car);
     return ax;
  }
}// cell<T>

// compile to .dll with csc /t:library polylists.cs