How to turn Koka effect control flow into an external iterator?

Koka has nice ways to model control flow with ctl effects:

pub fun main()    var n := 20    var sum := 0    (handler {        ctl yield(j) {            println(j)            sum := sum + j            n := n - 1            if n > 0            then resume(())        }    }){        fibonacci()    }    println("sum=" ++ sum.show)effect yield    ctl yield(i: int): ()fun fibonacci() : <div,yield> ()    var i := 0    var j := 1    yield(j)    while { True }        val k = i + j        i := j        j := k        yield(j)

(I'm sure this is not good Koka code but hopefully the question is still answerable)

What I want to achieve is to create an interator that can be polled to the next number. Something like:

fun next(iter: iterator): <console> maybe<int> 

Essentially to invert the control flow and poll values, so I can do other logic without putting it in the effect handler.