Some time ago I mentioned the Objective-C functional programming framework ReactiveCocoa.
Ryan Nystrom has written up an excellent in-depth tutorial detailing the basics of functional programming with ReactiveCocoa in the creation of a great looking weather app.
In addition to pointing out how to get start with functional programming in Objective-C the tutorial covers a number of recommend best practices, and shows how to download from the OpenWeatherMap API and use the data modeling framework Mantle.
Here’s an animation from the tutorial showing the final app in action:
A nice tutorial for those interested in functional programming, and learning some best practices from an experienced iOS developer.