Fault tolerant functional reactive programming (functional pearl)

Abstract

Highly critical application domains, like medicine and aerospace, require the use of strict design, implementation and validation techniques. Functional languages have been used in these domains to develop synchronous dataflow programming languages for reactive systems. Causal stream functions and Functional Reactive Programming capture the essence of those languages in a way that is both elegant and robust. To guarantee that critical systems can operate under high stress over long periods of time, these applications require clear specifications of possible faults and hazards, and how they are being handled. Modeling failure is straightforward in functional languages, and many Functional Reactive abstractions incorporate support for failure or termination. However, handling unknown types of faults, and incorporating fault tolerance into Functional Reactive Programming, requires a different construction and remains an open problem. This work presents extensions to an existing functional reactive abstraction to facilitate tagging reactive transformations with hazard tags or confidence levels. We present a prototype framework to quantify the reliability of a reactive construction, by means of numeric factors or probability distributions, and demonstrate how to aid the design of fault-tolerant systems, by constraining the allowed reliability to required boundaries. By applying type-level programming, we show that it is possible to improve static analysis and have compiletime guarantees of key aspects of fault tolerance. Our approach is powerful enough to be used in systems with realistic complexity, and flexible enough to be used to guide their analysis and design, to test system properties, to verify fault tolerance properties, to perform runtime monitoring, to implement fault tolerance during execution and to address faults during runtime. We present implementations in Haskell and in Idris. CCS Concepts: • Software and its engineering → Functional languages; • Hardware → Fault tolerance; • Theory of computation → Streaming models;

Runtime verification and validation of functional reactive systems

“…The study of how to introduce fault tolerance mechanisms in FRP systems was introduced in Perez (2018b) and Perez & Goodloe (2020), from which we borrow part of the introduction in this section and the introductory example that follows. We then extend that work to use temporal logic and QuickCheck to study the behaviour of a reactive system when faults are present in the system and to determine if fault tolerance mechanisms can handle faults as expected.…”

“…For further details on FRP, AFRP, and MSFs, see earlier papers (Elliott & Hudak, 1997;Nilsson et al, 2002;Courtney et al, 2003;. This presentation draws heavily from the summaries in Perez (2018b), Perez & Nilsson (2017) and Courtney et al (2003).…”

Fault-tolerant functional reactive programming (extended version)

“…This paper is an extended version of Perez (2018). Section 7 is an original contribution in this extended version, with examples from Perez et al (2019).…”