Implement a command-line program that asks the user to input a URL of some website, and displays the HTML of that website. Between the time that the user hits ENTER and the time that the HTML is retrieved, the program should repetitively print a . to the standard output every 50 milliseconds, with a two seconds timeout. Use only futures and promises, and avoid the synchronization primitives from the previous chapters. You may reuse the timeout method defined in this chapter.

Implement an abstraction called a single-assignment variable, represented by the IVar class:

class IVar[T] {
  def apply(): T = ???
  def :=(x: T): Unit = ???
}

When created, the IVar...