Javascript generators in Scala.js

Question

Currently I use Transcrypt to generate Javascript code from Python code. In this way I'm able to implement generators in Python like:

def color():
    colors = ["red", "blue", "yellow"]
    i = -1
    while True:
        i += 1
        if i >= colors.length:
            i = 0
        reset = yield colors[i]
        if reset:
            i = -1

gen = color()
console.log(next(gen)) # red
console.log(gen.js_next(True).value) # red
console.log(next(gen)) # blue
console.log(next(gen)) # yellow
console.log(next(gen)) # red

which will be compiled to Javascript like:

var color = function* () {
    var colors = list (['red', 'blue', 'yellow']);
    var i = -(1);
    while (true) {
        i++;
        if (i >= colors.length) {
            var i = 0;
        }
        var reset = yield colors [i];
        if (reset) {
            var i = -(1);
        }
    }
};
var gen = color ();
console.log (py_next (gen));
console.log (gen.next (true).value);
console.log (py_next (gen));
console.log (py_next (gen));
console.log (py_next (gen));

But since I have also Scala knowledge (and an Scala-application which I would like to implement in the browser) I'm looking to Scala.js. But as far as I know this generator construct is not possible in Scala, and the corresponding yield keyword is used in a different way.

Is the generator syntax possible in Scala.js, or am I forced to use Python and Transcrypt if I want this?

Answer 1

I believe the general concept you are looking for is Continuations. It's a fairly large and complex topic unto itself -- they used to be talked about more, but have largely been supplanted by the easier-to-use async library. But the scala-continuations library is still around, and discussed various places online -- for example, this article, or this one.