kotlin-generator-usage.kt

fun generator() = generate<Int, String> {
    var c = 1
    while (true) {
        val op = yield(c)
        when (op) {
            "inc" -> c += 1
            "mult" -> c *= 2
        }
    } 
}

fun main(args: Array<String>) {
    val g = generator()
    val a = g.next("") // start
    val b = g.next("inc")
    val c = g.next("mult")
    val d = g.next("inc")
    println("$a $b $c $d") // 1, 2, 4, 5
}