Lennart Augustsson has spent the last four decades quietly — and sometimes mischievously — shaping the way we think about code.

He co-authored Lazy ML in the early 80s, wrote A Compiler for LML back in 1984, and was behind HBC, the first publicly available Haskell compiler.

If you've used Haskell, worked with hardware described in Bluespec, or played around with weird combinator-based toy languages, there's a decent chance you've crossed paths with his ideas — directly or indirectly.

He's also won the International Obfuscated C Code Contest — not once, but multiple times — reminding us that playfulness and rigor aren't mutually exclusive.

But his work didn't stop in academia or hobby projects. He’s brought functional programming into finance, hardware design, large-scale industry — with stints at Credit Suisse, Facebook, Google, and now Epic Games, where he’s helping design a new functional logic programming language called Verse.

Over the course of this conversation, we’ll talk about lazy evaluation, type theory, programmable dungeons, the compromises of real-world programming, and what it means to still be building languages after 40 years in the game.

• Type Theory Forall Merch Store
• Ko-Fi
• Discord Server
• Haskell Interlude
• Lennart's Wikipedia Page
• Lennart's Webpage

In this episode we talk with Nicolas Tabareau, the Head of Gallinette, one of the main teams which develop the Rocq theorem Prover at Inria.

The original idea of this interview is to talk about the rebranding from Coq into Rocq, which is very exciting to our community. However, Nicolas has such a prolific research career that I couldn’t miss the opportunity to get him to talk so much more about it.

So in this conversation we talk about his early publications in neuroscience, his views on Category Theory applied to Type Theory, Rocq’s rebranding, and the institution around it, MetaRocq and the conceptual boundaries of certifying a theory inside itself. Of course we wouldn’t miss the opportunity to also discuss how Rocq view the growing influence that Lean is gaining in our community.

• Type Theory Forall Store
• Type Theory Forall Website
• Nicolas Tabareau Website
• MetaRocq Github

Wouter Swierstra is a Math Bachelor’s from the University of Utrecht, has done his PhD with Thorsten Altenkirch at the University of Nottingham, did a post-doc at Chalmers, has experience in the industry working on facilitating the design of embedded system using FP and currently is a Professor at the University of Utrecht and co-host of the Haskell Interlude Podcast.

In this episode we talk about his trajectory into formal methods and functional programming. We talk about Datatypes a la Carte, the Expression Problem, Functional Pearls, Program Synthesis vs Program Calculation, and much more!

0:00 – Intro & Welcome 0:02:08 – Announcing the Type Theory Forall Merch Store! 1:12 – Early Influences: From Lenses to Logic 4:40 – Discovering Functional Programming in Utrecht 8:15 – On Monads, Papers, and Learning by Teaching 12:20 – What Makes a Paper ‘Beautiful’? 17:50 – PhD in Nottingham: Theory Meets Community 22:00 – Writing ‘Certified Programming with Dependent Types’ 29:10 – Teaching Dependent Types: Challenges and Joys 34:00 – On Agda vs Coq: Philosophies and Use Cases 38:40 – Type-Driven Development in Practice 45:05 – The Power of Elegant Proofs 52:00 – Advice to Aspiring Researchers in Type Theory 1:03:00 – Beating C with Functional Programming 1:20:00 – Formal Verification and Loop Invariants 1:33:28 – Program Calculation vs Program Synthesis 1:39:00 – Formalizing Blockchain 2:01:38 – Final Thoughts

• Wouter Website

• Haskell Interlude

• Advanced FP Summer School

• ttforall twitch

• ttforall store

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