Crawler.scala

def workerFor(data: CrawlerData, url: Host): Task[(CrawlerData, MQueue[Url])] = {
  data.workers.get(url) match {
    case None =>
      val workerQueue = MQueue.make[Url]
      worker(workerQueue, crawlerQueue).map { workerFiber =>
        val workerData = WorkerData(workerQueue, workerFiber)
        val data2 = data.copy(workers = data.workers + (url -> workerData))
        (data2, workerQueue)
      }
    case Some(wd) => Task.now((data, wd.queue))
  }
}