class FileReader {
    output: TextBlock
    problem: TextBlock
    status: TextBlock
    task: Object
    function apply(self: FileReader): Unit {
        self.output.text = self.task.result()
    }
    function read(self: FileReader, path: String): Unit {
        self.task = ui.readText(self, "file", path, self.apply)
        self.output.text = ""
        self.status.bind("text", self.task.status)
        self.problem.bind("text", self.task.error)
    }
}
output = TextBlock("尚未读取文件")
problem = TextBlock("")
status = TextBlock("")
reader = FileReader(output, problem, status, ui.state(0))
page = Page()
page.title = "异步文件"
page.render(Column(24,16,TextBlock("在 REPL 调用 reader.read(绝对路径字符串)",2),status,output,problem))