The Beauty and Elegance of Functional Reactive Animation

Abstract

It has been over 20 years since Elliott and Hudak published Functional Reactive Animation, which outlined the principles of interactive programming in functional languages. As a result, Functional Reactive Programming (FRP) has seen numerous implementations and has been applied to multiple areas, like robotics, physics simulations, game programming and user interfaces. The use of the term FRP has itself broadened, and nowadays covers both continuous-time purely functional abstractions and discrete-time reactive implementations. This paper presents a series of increasingly complex FRP animations in a current implementation. With a main focus on clarity and meaning, we explore three independent dimensions: space, time, and color. We demonstrate that, when embraced fully, Functional Programming can result in declarative constructs that are aesthetically beautiful and notationally elegant.