Rhine: FRP with type-level clocks

Abstract

Processing data at different rates is generally a hard problem in reactive programming. Buffering problems, lags, and concurrency issues often occur. Many of these problems are clock errors , where data at different rates is combined incorrectly. Techniques to avoid clock errors, such as type-level clocks and deterministic scheduling, exist in the field of synchronous programming, but are not implemented in general-purpose languages like Haskell. Rhine is a clock-safe library for synchronous and asynchronous Functional Reactive Programming (FRP). It separates the aspects of clocking, scheduling and resampling from each other, and ensures clock-safety at the type level. Concurrent communication is encapsulated safely. Diverse reactive subsystems can be combined in a coherent, declarative data-flow framework, while correct interoperability of data at different rates is guaranteed by type-level clocks. This provides a general-purpose framework that simplifies multi-rate FRP systems and can be used for game development, media applications, GUIs and embedded systems, through a flexible API with many reusable components.

Fault-tolerant functional reactive programming (extended version)

“…Introducing an omissive fault would require a notion of asynchronicity, which can be incorporated into MSFs in multiple ways, the simplest of which would be make outputs optional with Maybe. Different ways of introducing asynchronicity in MSFs have been studied in Perez (2017) and Bärenz & Perez (2018).…”

“…Dependent probabilities can already be expressed in our proposal. Nevertheless, we expect to explore this further in the future, in combination with ongoing work on MSFs with type-level clocks (Bärenz & Perez, 2018) and integration with QuickCheck.…”

“…The essence of these languages can be captured via causal stream functions and some forms of functional reactive programming (FRP) (Elliott & Hudak, 1997;Nilsson et al, 2002;Courtney et al, 2003). While FRP has traditionally been applied to domains like interactive programming and games, abstractions like monadic stream functions (MSFs) (Perez et al, 2016;Perez, 2017;Bärenz & Perez, 2018) help bridge the gap between discrete-time causal stream programming and continuous-time FRP.…”

“…We later describe basic ideas from the field of fault tolerance, together with an example that illustrates the problems we seek to address. For further details, see earlier papers on FRP (Elliott & Hudak, 1997;Nilsson et al, 2002;Courtney et al, 2003) and MSFs (Perez et al, 2016;Perez, 2017;Bärenz & Perez, 2018). This presentation draws heavily from the summaries in Perez & Nilsson, (2017) and Courtney et al (2003).…”

Runtime verification and validation of functional reactive systems

“…From the point of view of the user, a change in the clock rate will imply both that the physics simulation is more accurate, and that the computers are sampling (and correcting) more frequently, but not necessarily help explain which one is at fault. The use of different clocks for FRP simulations and their correct coordination has been the subject of study of Bärenz & Perez (2018). Due to that solution being based on MSFs, the ideas discussed in this paper are directly applicable to simulations with multiple clocks.…”