/*
    algebraic data structures

    disadvantage: no destructive changes.

*/
import list.*;

class list<T>
{
   case nil;
   case cons(T head, list<T> tail);

   public String toString()
     {
       switch (this)
       {
	 case nil : return "\n";
	 case cons(T head, list<T> tail) : 
           return head+" "+tail.toString();
       }
     }  // toString();
}

public class thincrust
{

  public static void main(String[] args)
  {
    list<int> l = cons(2,cons(4,cons(6,nil)));
    System.out.print(l);
  }  
}