code: func (s *OrderedSet) Iter() <-chan string {
  	c := make(chan string)
  	go func() {
  		for _, i := range s.s {
  			c <- i
  		}
  		close(c)
  	}()
  
  	return c
  }
docs: // Iter returns a channel which yields the elements in this set in insertion
  // order.