title: PromiseKit with Swift: terminate chain of promises
body: <p>I'm trying to use PromiseKit with Swift. I am not really familiar with it, and there doesn't seem to be much information on its usage with Swift. </p>
  
  <p>I can't seem to figure out how to terminate a chain of promises. As long as the last (terminal) <code>then</code> block contains a single statement, everything is fine:</p>
  
  <pre><code>firstly {
      // ...
  }.then { obj in
      self.handleResult(obj)
  }.catch { error in
      self.handleError(error)
  }
  </code></pre>
  
  <p>However, if I try to add another statement, compiler complains:</p>
  
  <pre><code>firstly {
      // ...
  }.then { obj in
      self.handleResult(obj)
      self.doSomethingDifferent(obj)
  }.catch { error in // compiler error: Missing return in a closure expected to return 'AnyPromise'
      self.handleError(error)
  }
  </code></pre>
  
  <p>Obviously, the solution is to return another promise, but it doesn't make sense in the terminal block. Is there anything else I can do?</p>