Swift’s strong functional programming support leads to a lot of interest in adapting functional programming techniques to writing Cocoa applications. In particular, functional reactive programming (FRP) promises to replace unstructured side effects by structured change propagation in response to user input, network events, sensor activity, and similar. Typically explained by way of sophisticated, but often also complex functional reactive programming frameworks, such as ReactiveCocoa and RxSwift, it can be difficult to see the simple principles underlying functional reactive programming. In fact, these principles are sufficiently simple that we can explain them by building a functional reactive programming library from scratch. In this talk, I will illustrate how we can construct our own lightweight functional reactive programming library out of simple components using Swift’s support for protocol-oriented programming. Moreover, I will discuss how to use this library to design and implement the change propagation between the model and view components of a Cocoa app. All of this is illustrated with concrete Swift code taken from a simple iPhone application whose source code will be made available.

Manuel M T Chakravarty works with Tweag I/O as a functional programming evangelist, architects blockchain languages at IOHK, and develops the interactive development environment Haskell for Mac — one of the first Swift apps on the Mac App Store. His interests span from functional programming, novel compiler technology & programming language theory over high-performance & distributed computing to blockchain technology. He used to be an associate professor at UNSW Sydney and contributed to both the design and implementation of the Haskell programming language as well as several Haskell tools and open source libraries, including multiple systems for data parallel programming of multicore CPUs and GPUs. Over the last three years, he focused on making functional programming more broadly accessible and on exploring its role in app development in Swift. Most importantly, he believes in the fruitful combination of theory and practice.