It is important to understand FRP building blocks to be able to understand FRP. The following sections explain these building blocks with one of the great FRP libraries for the Cocoa framework, called ReactiveCocoa and its related library, ReactiveSwift, developed by GitHub. ReactiveCocoa was developed for Objective-C and, as of version 3.0, all major feature development is concentrated on the Swift API and all primitives are now a part of ReactiveSwift.

ReactiveSwift offers composable, declarative and flexible primitives that are built around the concept of streams of values over time. These primitives can be used to uniformly represent observation patterns. ReactiveCocoa wraps various aspects of Cocoa frameworks with the declarative ReactiveSwift primitives.