The Haskell Interlude

Mike and Andres sat down with Torsten Grust, who is a professor of DB systems at the University of Tübingen. Even though Torsten loves SQL, he's used functional programming and Haskell to inform his work on query language design and compilation. We talked about the best way to program databases, how to bridge the gap between regular programming languages and databases, and compiling just about everything to SQL. 

This is the first part of a miniseries on this year’s Symposium on Principles of Programming Languages, a.k.a. POPL 2026, hosted by Jessica Foster.In this episode, we talk about: undergrad funding and participation, the behind the scenes of AV, choreographic programming, quantum languages, conference catering, and the joy of theory. And at one point, you’ll even hear us get kicked out the venue mid interview. Enjoy!

Peter is a professor at the University of Freiburg, and he was doing functional programming right when Haskell got started. So naturally we asked him about the early days of Haskell, and how from the start Peter pushed the envelope on what you could do with the type system and specifically with the type classes, from early web programming to program generation to session types. Come with us on a trip down memory lane!

In this episode, we focus on a particular part of Haskell: teaching it. To help us, we are joined by Jamie Willis who is a Teaching Fellow at Imperial College London. The episode explores the benefits of live coding, and why Haskell is the best language for teaching programming.

Franz Thoma is Principal Consultant at TNG Technology Consulting, and an organizer of MuniHac. Franz sees functional programming and Haskell as a tool for thinking about software, even if the project is not written in Haskell. We had a far-reaching conversation about the differences between functional and object-oriented programming and their languages, software architecture, and Haskell adoption in industry. 

Welcome to the Haskell Interlude. Today, Matti and Mike talk toJeffrey Young. Jeff has had a long history of working with Haskell andon ghc itself. We talk about what makes Haskell so compelling, thegood and bad of highly optimized code and the beauty ofwell-modularized code, how to get into compiler development, and howto benefit from Domain-Driven Design.Jeff is currently on the job market - if you want to get in touch,email him at mailto:[email protected].

We are joined by Kathrin Stark, a professor at Heriot-Watt University in Edinburgh. Kathrin works on program verification with proof assistants, so her focus is not exactly on Haskell, but on topics dear to Haskellers' hearts such as interactive theorem provers, writing correct programs, and the activities needed to produce them. We discuss many aspects of proofs and specifications, and the languages involved in the process, as well as verifying and producing provably correct neural networks.

This episode is a deep dive into the evolution of Haskell and functional programming with one of its pioneers, Lennart Augustson. It  reflects on decades of work in language design and compiler implementation. Lennart speaks about his early involvement in the creation of Haskell, shares thoughts on type systems, performance, and the balance between purity and practicality. The conversation ranges from personal history to big-picture views on the evolution of programming languages, with plenty of insight into what makes Haskell both powerful and challenging. A rare opportunity to hear from one of the foundational voices in the functional programming world.

In this Interlude, we’re joined by Jean-Philipe Bernardy, a Senior Lecturer at University of Gothenburg and Chalmers University of Technology. We discuss letting types be your guide, getting into AI to feed yourself, and never testing your programs.

In this episode, we talk to Manuel Chakravarty - specifically, his work on the ghc backend such as data-parallel Haskell and the FFI  and how that work segued into type system design. We also discussed Manuel's perspective on Haskell from the language design of Swift.

Stefan Wehr is a professor at the Offenburg University of Applied Sciences. Before becoming a professor, Stefan worked in industry on a large Haskell codebase - specifically one that's not a compiler and not a blockchain. So of course we talked about using Haskell in large projects, software architecture, modularity, type classes and data modeling and the suppression of sums outside of functional programming, and also about teaching Haskell at his current job.

We sat down with Phil Wadler, one of the most influential folks in the Haskell community, functional programming, and programming languages, responsible for type classes, monads, and much more. We take a stroll down memory lane, starting from Haskell's inception. We talked about the difference between research and Phil's work on impactful industrial projects and standards - specifically XML and the design of generics in Java, as well as Phll's teaching at the University of Edinburgh using Agda.. Phil is a fountain of great ideas and stories, and this conversation could have gone on for hours. As it is, we hope you enjoy the hour that we had as much as we did. 

Today’s guest is Jurriaan Hage. Jurriaan is a professor at Heriot-Watt University in Edinburgh who’s worked with and on Haskell for many years. He’s known for the Helium Haskell compiler, specifically designed for teaching, and he has plenty of other projects related to Haskell, including improvements to the type system, the generation of better error messages, or detection of plagiarism. 

In this episode, we’re joined by Michael Snoyman, author of Yesod, Conduit, Stackage and many other popular Haskell libraries.We discuss newcomer friendliness, being a Rustacean vs a Haskellasaur, how STM is Haskell’s best feature and how laziness can be a vice.

Mike and Andres speak to Alex McLean who created the TidalCycles system for electronic music - implemented in Haskell of course. We talk about how Alex got into Haskell coming from Perl, how types helped him think about the structure of music and patterns, the architecture and evolution of TidalCycles, about art, community and making space for new ideas, and lots of things in between.

Niki and Mike talked to Daniele Micciancio who is a professor at UC San Diego. He's been using Haskell for 20 years, and works in lattice cryptography. We talked to him about how he got into Haskell, using Haskell for teaching theoretical computer science and of course for his research and the role type systems and comonads could play in the design of cryptographic algorithms. Along the way, he gave an accessible introduction to post-quantum cryptography which we really enjoyed. We hope you do, too. 

Andy Gordon from Cogna is interviewed by Sam and Matti. We learn about Andy’s influential work including the origins of the bind symbol in haskell, and the introduction of lambdas in Excel. We go onto discuss his current work at Cogna on using AI to allow non-programmers to write apps using natural language. We delve deeper into the ethics of AI and consider the most likely AI apocalypse.

In this episode Mike Sperber and Niki Vazou talk with Sandy Maguire, lead compiler engineer at Manifold Valley. They talk about the benefits of using Haskell of course, about all the books Sandy has written, on effects and the problem with monads, on combinator libraries and programming with laws.

On this episode of the Haskell Interlude, Andres Löh and Mike Sperber are joined by Farhad Mehta, a professor at OST Rapperswil, and one of the organizers of ZuriHac. Fahrad tells us about formal methods, building tunnels, the importance of education, and the complicated relationship between academia and industry.

In this episode Wouter Swiestra and Niki Vazou talk with Conal Elliott. Conal discusses doing things just for the poetry, how most programs miss their purpose, and the simplest way to ask a question. Conal is currently working on a book about his ideas and actively looking for partners. 

Sam Lindley is a Reader in Programming Languages Design and Implementation at the University of Edinburgh. In this episode, he tells us how difficult naming is, the different kinds of effect systems and handlers, languages *much* purer than Haskell, and Modal logic.

Tom Ellis works at Groq, using Haskell to compile AI models to specialized hardware.  In this episode, we talk about stability of both GHC and Haskell libraries, effects, and strictness, and the premise of functional programming: make invalid states and invalid *laziness* unrepresentable! 

Sam and Wouter interview Harry Goldstein, a researcher in property-based testing who works in PL, SE, and HCI. In this episode, we reflect on random generators, the find-a-friend model, interdisciplinary research, and how to have impact beyond your own research community.

In this episode, Matti and Sam traveled to the International Conference on Functional Programming (ICFP 2024) in Milan, Italy, and recorded snippets with various participants, including keynote speakers, Haskell legends, and organizers.

Gabriele Keller, professor at Utrecht University, is interviewed by Andres and Joachim. We follow her journey through the world as well as programming languages, learn why Haskell is the best environment for embedding languages and how the desire to implement parallel programming sparked the development of type families in Haskell and that teaching functional programming works better with graphics.

Today on the Haskell Interlude, Matti and Sam are joined by Satnam Singh. Satnam has been a lecturer at Glasgow, and Software Engineer at Google, Meta, and now Groq. He talks about convincing people to use Haskell, laying out circuits and why community matters.PS: After the recording, it was important to Satnam to clarify that his advise to “not be afraid to loose your job” was specially meant to encourage to quit jobs that are not good for you, if possible, but he acknowledges that unfortunately not everybody can afford that risk.

In this episode, Niki and Andres talk with Sebastian, one of the main developers of Lean, currently working at the Lean Focused Research Organization. Today we talk about the addictive notion of theorem provers, what is a sweet spot between dependent types and simple programming and how Lean is both a theorem prover and an efficient general purpose programming language. 

In this episode, Wouter and Sam interview Dominic Orchard. Dominic has many roles, including: senior lecturer at the University of Kent, co-director of the Institute of Computing for Climate Science, and bye-fellow of Queen’s College in Cambridge. We will not only discuss his work on Granule - graded monads, coeffects, and linear types - but also his collaboration with actual scientists to improve the languages with which they work.

In this episode, Garrett Morris talks with Wouter Swierstra  and Niki Vazou about his work on Haskell’s type classes, how to fail successfully, and how to construct a set of ponies.

Andres and Sam interview Pepe Iborra, exploring his journey from academia via banking to now Meta. In this episode, we discuss Pepe’s involvement in the evolution of the Haskell ecosystem, in particular the ongoing journey to improve the developer experience via work on debuggers, build systems and IDEs.

Victor Miraldo is interviewed by Niki and Joachim and walks us through this career from a student falling in love with List.foldr through a PhD student using agda to verify cryptographic data structures and generic diff and merge algorithms to a professional developer using Haskell in production. He’ll tell us why the Haskell community is too smart, why there should be a safePerformIO, and that he hopes that Software Engineering could be less like alchemy.

In this episode Tom Sydney is chatting with Matti Paul and Niki Vazou. Tom is the author of many tools, like sydtest, decking, and nix-ci. He tells us about the rules for sustainable Haskell, how Haskell lets one man do the job of 50, and the secret sauce for open source.Tom Sydney is also looking for work these days, so get in touch!

Wouter and Joachim interview Arseny Seroka, CEO of Serokell. Arseny got into Haskell because of a bet over Pizza, fell for it because it means fewer steps between his soul and his work, and founded Serokell because he could not get a Haskell job. He speaks about the business side of a Haskell company, about the need for more sales and marketing for Haskell itself, and about the Haskell Developer Certification.

In this episode, Andres Löh and Matthías Páll Gissurarson interview José Nuno Oliveira, who has been teaching Haskell for 30 years. José talks about how Haskell is the perfect language to introduce programming to all sorts of audiences, why it is important to start with Haskell, and how the programmers of the future have been learning Haskell for several years already!

Avi Press is interviewed by Joachim Breitner and Andres Löh. Avi is the founder of Scarf, which uses Haskell to analyze how open source software is used. We’ll hear about the kind of shitstorm telemetry can cause, when correctness matters less than fearless refactoring and how that can lead to statically typed Stockholm syndrome.

Roman, known better online as effectfully, is interviewed by Wouter and Joachim. On his path to becoming a Plutus language developer at IOG, he learned English to read Software Foundations,   has encountered many spaceleaks, and used Haskell to prevent robots from killing people.

In this episode, András Kovács is being interviewed by Andres Löh and Matthias Pall Gissurarson. We learn how to go from economics to functional programming, how GHC's runtime system is superior to Rust's, the importance of looking at GHC's Core for spotting stray closures, and why staging might be the answer to all your optimisation problems.

Wouter and Niki interview Jose Calderon, the new Executive Director of the Haskell Foundation. Jose tells why he applied for the job, how he sees the foundation developing over the coming years, and how you can get involved in the Haskell community.

In this episode, Wouter and Andres interview Ivan Perez, a senior research scientist at NASA. Ivan tells us about how NASA uses Haskell to develop the Copilot embedded domain specific language for runtime verification, together with some of the obstacles he encounters getting to end users to learn Haskell and adopt such an EDSL.

Jezen Thomas is co-founder and CTO of Supercede, a company applying Haskell in the reinsurance industry. In this episode, Jezen, Wouter and Joachim talk about his experience using Haskell in industry, growing a diverse and remote team of developers, and starting a company to create your own Haskell job.

Today, Matthías and Joachim are interviewing Moritz Angermann. Moritz knew he wanted to use Haskell before he knew Haskell, fixed cross-compilation as his first GHC contribution. We’ll talk more about cross-compilation to Windows and mobile platforms, why Template Haskell is the cause of most headaches, why you should be careful if your sister calls and tells you to cabal install a package, and finally how we can reduce the fear of new GHC releases, by improving stability.

In this episode, Andres and Matti talk to Mike Sperber, CEO of Active Group in Germany. They discuss how to successfully develop an application based on deep learning in Haskell, contrast learning by example with the German bureaucratic approach, and highlight the virtues of having fewer changes in the language.

In this episode, we are joined by Rebecca Skinner. She talks about her new book, Effective Haskell, which takes you from list manipulation to thunks to type-level programming. She also tells us about large scale industrial applications in Haskell, and how the architecture is shaped by the organization of the engineering teams.Disclaimer: Mercury is a financial technology company, not a bank. Banking services provided by Choice Financial Group and Evolve Bank & Trust, Members FDIC.

Andres and Wouter interview Edwin Brady, most famous for his work on the Idris programming language. We talk about how he got interested in programming with dependent types, his thoughts on dependently typed programming in Haskell, and his vision for Idris.

Joachim Breitner and David Thrane Christiansen interview John MacFarlane, a professor of philosophy at UC Berkeley, but also the author of the popular pandoc document conversion tool, which has been around half as long as Haskell itself.He also explains the principle of uniformity as a design goal for lightweight markup languages, the relationship between philosophy and programming, and along the way he helps David with his markdown difficulties.

In this episode, Matti and Wouter are joined by John Hughes. John is one of the authors of the original Haskell Report and talks about why functional programming matters, the origins of QuickCheck testing, and how higher order functions and lazy evaluation is the key that makes functional programming so productive, and so much fun!

Wouter and Niki are joined by Iavor Diatchki to talk about his experience with different Haskell development styles, writing a high assurance wiki in php, and maintaining Haskell code across different GHC releases over multiple decades.

In this episode Niki Vazou and Wouter Swierstra chat with Lindsey Kuper, Assistant Professor at University of California, Santa Cruz. They discuss what to do when your data center gets hit by a tornado, life in academia versus life in industry, and what is choreographic programming. 

In this farewell interview with David Thrane Christiansen, the outgoing Executive Director of the Haskell Foundation, hosts Wouter Swierstra and Matthías Páll Gissurarson use the opportunity to reflect on his tenure as ED, the recent history of the Haskell Foundation, where the HF is going and what consider if you want to apply for the role of Executive Director of the HF.

This episode’s guest is Ranjit Jhala. We discuss how Ranjit developed Liquid Haskell as a litmus test, because if Haskell programmer’s won’t use Liquid Types, no one will. We also hear how writing Haskell is a joy and how you should never underestimate your students.