Functional programming and blockchains are a match made in heaven! The immutable and reproducible nature of distributed ledgers is mirrored in the semantic foundation of functional programming. Moreover, the concurrent and distributed operation calls for a programming model that carefully controls shared mutable state and side effects. Finally, the high financial stakes often associated with blockchains suggest the need for high assurance software and formal methods.

Nevertheless, most existing blockchains favour an object-oriented, imperative approach in both their implementation as well as in the contract programming layer that provides user-defined custom functionality on top of the basic ledger. On the one hand, this might appear surprising, given that it is widely understood that this style of programming is particularly risky in concurrent and distributed systems. On the other hand, blockchains are still in their infancy and little research has been conducted into associated programming language technology.

In this talk, I will explain the connection between blockchains and functional programming as well as highlight several areas where functional programming, type systems, and formal methods have the potential to advance the state of the art. Overall, I will argue that blockchains are not just a well-suited application area for functional programming techniques, but that they also provide fertile ground for future research. I will illustrate this with evidence from the research-driven development of the Cardano blockchain and its contract programming platform, Plutus. Cardano and Plutus are implemented in Haskell and Rust, and the development process includes semi-formal specifications together with the use of Agda, Coq, and Isabelle to formalise key components.

Manuel M T Chakravarty published extensively on programming languages, compilers, and high-performance computing. He contributed to both the design and implementation of the Haskell programming language (most notably, type families, associated types, and the foreign function interface) as well as several Haskell tools and open source libraries. He used to be an Associate Professor at UNSW Sydney, but with the increasing adoption of functional programming in industry, he shifted his focus to unlocking new application areas for functional programming and helping development teams reap the benefits of modern programming language technology. He is currently a technical evangelist at Tweag I/O and co-leading the research-driven Plutus smart contract language team at IOHK.