fun doStuff(msg: String, done: (a: String, b: Int) -> Unit) {
    var newMsg = "hackkkk! " + msg // params are always read-only
    done(newMsg, 3)
}

fun main(args: Array<String>) {
    doStuff("halo vurld", { a, b ->
        for (i in 0..b) println(a)
    })
}

/*
Output:

hackkkk! halo vurld
hackkkk! halo vurld
hackkkk! halo vurld
hackkkk! halo vurld
*/