We've recently started using ReactiveCocoa in the Venmo iOS app, and we've found that it provides an expressive, unified alternative to patterns like callback blocks, delegate methods, target-action, notifications, and KVO. If you haven't heard of ReactiveCocoa or Functional Reactive Programming (FRP), we recommend starting with this awesome post by Josh Abernathy and the official introduction. In
![Blissful UI programming with ReactiveCocoa](https://cdn-ak-scissors.b.st-hatena.com/image/square/f38fbd634f489fff3bc596cce842602d5ff038a3/height=288;version=1;width=512/http%3A%2F%2Fvenmo.github.io%2Fimages%2Freactive_signup.png)