class Unfoldr<A,B> implements java.util.Iterator<A>
{
  public Unfoldr(Closure<Tuple> f, B init) 
  {
    this.f = f;
    this.state = f(init);
  }
 
  public synchronized A next() 
  {
    if (hasNext())
    {
      A curr = state.get(0);
      state = f(state.get(1));
      return curr;
    }
    else
    {
      throw java.lang.NoSuchElementException;
    }
  }
 
  public synchronized boolean hasNext() 
  {
    return (state != null);
  }
 
  public void remove() { throw UnsupportedOperationException; }
 
  private Closure<Tuple> f;
 
  private Tuple state;
}
 
def unfoldr = { f, init -> new Unfoldr(f, init) };
 
def u = unfoldr({ x -> if (x < 100) { new Tuple(x + 1, x + 1) } else null; }, 0);
 
for(e in u)
{
  print e;
  print "\n";
}
 

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