Excellent, easy to understand for old fashioned programmers, the introductory lecture that Sam Ruby does about continuations, Continuations for Curmudgeons.

Brian McCallister writes about guidelines to write webapps, including a reference to the concept Modal Webapps, what Stefano has been doing for years using continuations first with scheme and later with javascript.

By coincidence, I have been preparing my lesson on iterators for the University classes about the time I was reading those entries. I decided to give the students the simple example about generators that Sam gives, slightly changed to put the generator's end inside the generator itself:

def fib(max=1000):
  """Devuelve un generador para n. de Fibonacci"""
  yield 0
  i,j = 0,1
  while j<max:
    yield j
    i,j = j,i+j
  raise StopIteration

if __name__ == "__main__": 
  for n in fib():
    print n

This compares very naturally with the implementation as java Iterators of the same code, except that java types get often in the way, and it is fairly more verbose:

import java.util.Iterator;

public class Fibonacci implements Iterator {

	private int i=0;
	private int j=1;
	private int max;
		
	public Fibonacci(int max) {
		this.max = max;
	}
	
	public Fibonacci() {
		this(1000);
	}

	public boolean hasNext() {
		return j < max;
	}

	public Object next() {
		Integer result = new Integer(j);
		int temp = i;
		i = j;
		j = j + temp;
		return result;
	}

	public void remove() {
		throw new UnsupportedOperationException("No soportado");
	}

	public static void main(String[] args) {
		Iterator it = new Fibonacci();
		while(it.hasNext()){
			System.out.println(it.next());
		}
	}
}

Both python generators and java iterators would allow us to write portlets in a very natural way, except that the back button would be forbidden. But it is nonetheless mostly unusable in portlets anyway, so it is not a big lose.

I'm waiting for jython to have generators (i.e, to be 2.3) to try an embedded jython interpreter to write portlets. I'm thinking that, while this comes, writing a HttpPortletRequestIterator and toying how easy it is to write portlets using it would be a win.