class TextFetcher {
    output: TextBlock
    problem: TextBlock
    status: TextBlock
    task: Object
    response: String
    function apply(self: TextFetcher): Unit {
        self.response = self.task.result()
        self.output.text = "请求完成；在 REPL 查看 fetcher.response"
    }
    function fetch(self: TextFetcher, url: String): Unit {
        self.task = ui.fetchText(self, "request", url, self.apply)
        self.response = ""
        self.output.text = ""
        self.status.bind("text", self.task.status)
        self.problem.bind("text", self.task.error)
    }
}
output = TextBlock("尚未请求网络")
problem = TextBlock("")
status = TextBlock("")
fetcher = TextFetcher(output, problem, status, ui.state(0), "")
page = Page()
page.title = "异步网络"
page.render(Column(24,16,TextBlock("在 REPL 调用 fetcher.fetch(HTTP 或 HTTPS 地址字符串)",2),status,problem,output))