code: public <E> S forEach(Fx<S, E> functor) {
  		return forEach(null, functor);
  	}
docs: Iterates over the collection elements or entries and passing each of them
  to the given implementation of the functor interface; if state needs to be
  propagated, it can be instantiated and returned by the first invocation of
  the functor and it will be passed along the next elements of the collection.
  
  @param functor
  an implementation of the {@code $} functor interface.
  @return
  the result of the iteration.