using System;

public delegate Mapper[T,V] (mutable  item : T) :  V;

public interface ITree[T]
{
   Map[V] (mutable  mapper : Mapper[T,V]) : void;
}

public class Tree[T] : ITree[T]
{
   mutable  item : T;

  public this (mutable  item : T)
  {
    this.item = item;
  }

  public Map[V] (mutable  mapper : Mapper[T,V]) :  void
  {
    def _new_item = mapper (item); ();
  }
}

class X
{
  private themap (mutable  i : int) :  string
  {
     String.Format ("AA {0,4} BB", i);
  }

   Test () : void
  {
    mutable  tree =  Tree (3);
    tree.Map ( Mapper (themap));
  }

  static Main () :  void
  {
    mutable  x =  X ();
    x.Test ();
  }
}
/*
BEGIN-OUTPUT
END-OUTPUT
*/