Scala演员：如果反应没有返回,为什么需要循环{},为什么不(true)

Thread-blocking operations can be avoided by using react to wait for
new messages (the event-based pendant of receive). However,there is a
(usually small) price to pay: react never returns.

…

Note that using react inside a while loop does not work! However,
since loops are common there is special library support for it in form
of a loop function. It can be used like this:

loop {
  react {
    case A => ...
    case B => ...
  }
}

我现在很困惑 – 似乎有一个矛盾：

a)如果反应没有返回,那么把它放在一个循环中是什么意思？

b)由于循环重复执行一个块,它与…(true)有什么不同 – 为什么不工作,以什么方式“不工作”？