tailrec fun <T, R> Iterable<T>.mapWithConsIter(result: Cons<R>, src: Iterator<T>, cb: (T) -> R): List<R> {
    if (!src.hasNext()) {
        return result
    }
    val e = src.next()
    return mapWithConsIter(Cons<R>(cb(e), result), src, cb)
}