Once we formalize the syntax of a language, the next step is to formalize its semantics: what programs mean and how they behave. There are three classical approaches. 1) Operational semantics Operational semantics defines meaning by describing how programs execute on an abstract machine. 1/8

In a few minutes we are going live on Twitch to watch and discuss selected ICFP talks together. If you are interested in programming languages research, semantics, type systems, and formal methods, join us for a live session of collective viewing and commentary.

going to do some #LeanLang streaming for the first time in a while! i tried to get claude code to add polymorphism to my formalisation of HM. let's see what it managed to do and where it got stuck. join me as i do some forensic analysis 🕵️ starting at 7:30pm UTC today! www.twitch.tv/aronadler

90+ hours interviewing the best minds in type theory. Now you can wear (and sip from) the movement. The Type Theory Forall store is up and running. Apparel and mugs for people who care about foundations. Every purchase helps keep deep PL conversations alive. https://twp.ai/9PbfTY

New semester just started. If your Rocq file already has 37 unsolved goals If your compiler project looks… concerning I’m opening tutoring spots in: • Rocq • Haskell / OCaml • Compilers • Logic & Algebra Strong foundations. No shortcuts. Free intro call 👇

90+ hours interviewing the best minds in type theory. Now you can wear (and sip from) the movement. The Type Theory Forall store is up and running. Apparel and mugs for people who care about foundations. Every purchase helps keep deep PL conversations alive. https://twp.ai/9PbTgF

"Readable formal specifications are not a convenience that AI can replace. They are the foundation of trust."

People often ask: what is type theory and why is it useful? Type Theory is the academic study of type systems: formal frameworks for classifying terms, structuring computation, and specifying the behavior of programs. 🧵 1/9

I’m planning next month’s Type Theory Forall episodes and I’d genuinely love your input. What would you be interested to hear next? Proof theory? Modern Programming Language Semantics? Lean or Rocq? Compilers? AI × formal methods? Is there a paper, idea, or person you think I should talk to?

90+ hours interviewing the best minds in type theory. Now you can wear (and sip from) the movement. The Type Theory Forall store is up and running. Apparel and mugs for people who care about foundations. Every purchase helps keep deep PL conversations alive. https://twp.ai/9PbYfP

An ode to the International PhD Student "To the one living between time zones. Between ambition and homesickness. Between gratitude and guilt. " https://twp.ai/9PbVnL

New semester just started. If your Rocq file already has 37 unsolved goals If your compiler project looks… concerning I’m opening tutoring spots in: • Rocq • Haskell / OCaml • Compilers • Logic & Algebra Strong foundations. No shortcuts. Free intro call 👇

90+ hours interviewing the best minds in type theory. Now you can wear (and sip from) the movement. The Type Theory Forall store is up and running. Apparel and mugs for people who care about foundations. Every purchase helps keep deep PL conversations alive. https://twp.ai/9PbYcf

I was at AmeriHac this past weekend! Decided to write up a blogpost about it :D I did my best to capture the experience. Please let me know if there are any errors or if you have any comments, suggestions or questions thedeveloper101.github.io/posts/2026/0...

ZuriHac 2026 - Registrations are open! ZuriHac is the biggest Haskell community event in the world: a completely free, three-day grassroots coding festival co-organized by the Zürich Friends of Haskell and the OST Eastern Switzerland University of Applied Science. Register: zureg.zfoh.ch/register

ZuriHac also welcomes beginners or people unfamiliar to Haskell who are curious to learn more. There will be an organized beginners’ track, as well as many mentors from the Haskell community happy to answer all your questions.

Your proof assistant is strict. Your type system is expressive. Your coffee mug should be too ☕ FP & ITP mugs (OCaml, Haskell, Lean, Rocq, Isabelle, Agda): store.typetheoryfora...

Type Theory Forall exists because this community exists. If the podcast, the conversations, or the ideas mattered to you, this is one way to support it — and look good doing it 👕 👉 store.typetheoryfora...

New TTFA episode 🎙️ The category-theoretic episode we’ve ever done. A deep dive into Category Theory, Type Theory, and Logic with Valeria de Paiva — co-founder of the Topos Institute and founder of Women in Logic.

Your proof assistant is strict. Your type system is expressive. Your coffee mug should be too ☕ FP & ITP mugs (OCaml, Haskell, Lean, Rocq, Isabelle, Agda): store.typetheoryfora...

Type Theory Forall exists because this community exists. If the podcast, the conversations, or the ideas mattered to you, this is one way to support it — and look good doing it 👕 👉 store.typetheoryfora...

Your proof assistant is strict. Your type system is expressive. Your coffee mug should be too ☕ FP & ITP mugs (OCaml, Haskell, Lean, Rocq, Isabelle, Agda): store.typetheoryfora...

Type Theory Forall exists because this community exists. If the podcast, the conversations, or the ideas mattered to you, this is one way to support it — and look good doing it 👕 👉 store.typetheoryfora...

Your proof assistant is strict. Your type system is expressive. Your coffee mug should be too ☕ FP & ITP mugs (OCaml, Haskell, Lean, Rocq, Isabelle, Agda): store.typetheoryfora...

Type Theory Forall exists because this community exists. If the podcast, the conversations, or the ideas mattered to you, this is one way to support it — and look good doing it 👕 👉 store.typetheoryfora...

Your proof assistant is strict. Your type system is expressive. Your coffee mug should be too ☕ FP & ITP mugs (OCaml, Haskell, Lean, Rocq, Isabelle, Agda): store.typetheoryfora...

Type Theory Forall exists because this community exists. If the podcast, the conversations, or the ideas mattered to you, this is one way to support it — and look good doing it 👕 👉 store.typetheoryfora...

In case you missed it, watch this clip from our interview with Andrej Bauer. I love when CS researchers can articulate a philosophy behind their work, and Andrej DELIVERS www.youtube.com/watch?v=GcTF...

🎉 5 YEARS OF TYPE THEORY FORALL 🎉 To celebrate, I sat down with Andrej Bauer. Student of Dana Scott. A mind equally at home in math and CS. One of the clearest thinkers in Type Theory. We dive into Constructivism, Dialectica, Effect Handlers, and AI. This one is special.

🎙️ New Type Theory Forall Episode! #57 — Compilers for Privacy-Preserving Computation, Category Theory, and Keeping a Good Rhythm in Your PhD This week I talk with Rhagav Malik, fresh off his PhD defense on compilers for privacy-preserving computation. We dig into:

My Spotify Wrapped

Going live now! Continuing our Lean 4 Series — today we continue working on MIL, this time on Order and divisibility! This is part of our ongoing fundraiser to replace my iPhone camera with a proper setup. Every tip helps! ☕️ko-fi.com/typetheory... www.twitch.tv/typeth...

Last days of our Cyber Monday 15% OFF at the ttfa store! Mugs, hoodies, shirts — perfect gifts for your nerdiest friends this holiday season. Enjoy it before it ends: store.typetheoryfora...

A couple weeks ago I had the great pleasure of inviting Rustan Leino (of Dafny fame) on my podcast, to talk about all sorts of logic stuff! Part II to come soon! open.spotify.com/episode/4d9J...

A fresh episode of Type Theory Exists is live! Featuring my Gothenburg talk on the evolution of CS through the eyes of Type Theory — Turing, Church, Curry–Howard, and beyond. 🔒 Only for patrons — join us to unlock it:

🚨 BLACK FRIDAY SALE! 🚨 The entire Type Theory Forall shop is 15% OFF — mugs, shirts, hoodies, literally everything. Only until the end of the month. Don’t miss it! 🛒🔥 store.typetheoryfora... Discount is automatically applied at checkout.

@krismicinski's build a compiler in Five Projects

My five-project (along with slides, video lectures, etc.) compilers course has all projects now available online free: kmicinski.com/functional-p.... Five projects have you incrementally build a compiler for a substantial language, including functions, mutation, loops, vectors, etc.

Going live now! Continuing our Lean 4 Series — today I'll start working on Mathematics in Lean This is part of our ongoing fundraiser to replace my iPhone camera with a proper setup. Every tip helps! 💜 ☕️ko-fi.com/typetheory... www.twitch.tv/typeth...

🚨 BLACK FRIDAY SALE! 🚨 The entire Type Theory Forall shop is 15% OFF — mugs, shirts, hoodies, literally everything. Only until the end of the month. Don’t miss it! 🛒🔥 store.typetheoryfora... Discount is automatically applied at checkout.

Going live now! Continuing our Lean 4 Series — today I’ll be learning Tactics on stream. This is part of our ongoing fundraiser to replace my iPhone camera with a proper setup. Every tip helps! 💜 ▶️ www.twitch.tv/typetheoryfo... ☕️ ko-fi.com/typetheoryfo...

A new book on the history of control structures by the creator of #OCaml himself @camlist.bsky.social xavierleroy.org/control-stru...

Feeling the pull back to academia? Whether you’re applying for grad school or looking to transition from industry into research, our mentorship program can guide you. We still have open slots for this season! → typetheoryforall.com/mentorship

types slow me down in the way that red lights slow me down when i'm driving

Pedro Abreu aka #TypeTheoryForall had an epic conversation with me about all things programming languages, out now on the podcast. www.typetheoryforall.com/episodes/the...

#LiquidTypes are a lightweight way to specify and check code properties. What stands in the way of more widespread adoption? Today at #SPLASH 2025 / @icfp-conference.bsky.social: @catarinavgamboa.bsky.social will re-present our #PLDI2025 paper on Usability Barriers for Liquid Types.

We still have a few spots open this week for 1:1 mentorship sessions on grad school applications and research careers. If you’re applying to PhD programs or navigating advisor selection, this might be the perfect time to start. 👉 typetheoryforall.com/mentorship

true friendship 🥹

How do we know that the semantics of a programming language are right? My latest Programming Language Pragmatics video covers type soundness: the static and dynamic semantics of a language fit together, so that if a program type checks, it will not experience unexpected type errors when it runs.