I've been telling people for 25 years that Jane Street is not interested in formal methods. No more! And we're actively hiring to form a new formal methods team! blog.janestreet.com/formal-metho...

This is a fairly wild post about OxCaml Labs from @avsm . It's hard to summarize the stuff they're doing, but, some examples: - Some wild vibecoding - A formal semantics for package managers - A decade of docker containers (including OxCaml!?!) anil.recoil.org/projects/oxc...

Another fun hiring spot at Jane Street: we're looking to hire some great hybrid writers-and-engineers. As we grow and do more, communication becomes ever more important, for both internal and external audiences. www.janestreet.com/join-jane-st...

It's been a minute, but, time for another Signals and Threads, this one with Will Wilson about the testing tools he's building at @antithesis.com. And, in a bow to modernity, we have a video version of this one too! youtu.be/F_LvzcdNH3Q?...

A poor craftsman blames his tools. Wealthy craftsmen also blame their tools. Lots of tool-blaming going around.

I wonder if we're starting to hit a deflationary era in software engineering. For the first time, we're starting to talk about this in a planning context; it can make sense to put off some projects because we expect they'll be easier to achieve in the future than today.

Seems like a good time as any to say I'm: (1) moving to New York next week, where I'll: (2) be writing OxCaml at Jane Street! Excited to start the next thing :)

February 10th, and thus the inaugural edition of NINeS is just around the corner. You can participate from anywhere in the world, at times that are convenient to you. See https://nines-conference.org/attend for information on how you can participate. We hope to see you on Feb 10th!

My regular PSA that if you enjoy working on developer tools, then Jane Street is kind of an amazing place. Apply here! There's no special posting, so just apply for the Software Engineering role, and express your interests in dev-tools in a note. janestreet.com/apply

We've had an exciting couple of weeks full of opportunities to teach people about the exciting (and mildly bewildering) features of OxCaml. And...we're looking to hire an experienced educator to help us in this work. Please share this with anyone you think might be a good fit!

I did anothr version of my "Saga of Mulicore OCaml" talk, but this time, nerve-wrackingly, the authors of the original paper were all there! Here's the link to the talk, which is found towards the end of the recording for the whole session. t.co/FQTmsFWji0

Me too! (But Max knows more about it than I do.)

Most companies be like “We daren’t go functional, we might not be able to hire”. Jane Street be like “Hold. Our. Beer.”

Excited to say that we're looking to hire someone to focus on OxCaml education! We're doing enough to change the language that we have a pretty big internal education task ahead of us, and we want to hire someone to focus on it! Please share this with others! www.janestreet.com/join-jane-st...

A fun talk about...hacking OCaml. Basically, what you get when you supercollide a systems-y OCaml developer and a CTF. www.youtube.com/watch?v=SV9V...

On Advisory Opinions, Sarah Isgur and David French speak with me about enumerated powers. The segment begins 43-44 minutes in, depending on format. This was a good conversation among people with different approaches to constitutional interpretation. thedispatch.com/podcast/advi...

They should know the difference between TeX and LaTeX, so they could hate Lamport less and Knuth more.

Clearly, the reason for the AI work is to build an AI capable of porting from Latex to Typst.

"we need a manhattan project for AI" no what we really need is a manhattan project for porting every math TeX package to Typst (and please start with mathpartir)

I've raised my kids well, I think.

A new episode of Signals and Threads just dropped! This one is an interview with Chris Lattner talking about Mojo, a new-ish language for GPU programming that's aiming to be an alternative to the CUDA stack. signalsandthreads.com/why-ml-needs...

This was a great talk from Will Crichton. I think Will's approach to approaching questions around language tooling and teaching is compelling, though I wonder how far the approach can scale! youtu.be/R0dP-QR5wQo?...

I just finished our yearly roundup of this year's intern projects, and it was a real bumper crop! Lots of fun projects, and some cameos from OxCaml... blog.janestreet.com/wrought-2025/

Just ran across this old post from a former intern about Jane Street's approach to programming and code review. I thought it was a pretty accurate, and I think captures something important about how OCaml's design makes code review easier and more effective. digitalfreepen.com/2017/01/07/j...

This will remove so many unnecessary OCaml functors from our codebases. My rough rule of thumb is that if a functor is not applied more than once in a codebase, it doesn’t need to be a functor. Parameterised libraries lets us easily do one-shot reuse of existing modules in a different context.

We've finally landed a full version internally (coming to an OxCaml near you soon!) of a new feature called parameterized libraries. It's basically an answer to a problem I first ran into 23 years ago. Here's a thread about it on the caml-list. inbox.vuxu.org/caml-list/10...

A new epsiode of Signals and Threads has just dropped: "The Thermodynamics of Trading". I got to talk to Dan Pontecorvo from our physical engineering team about the complex work that goes into our physical spaces to make the work we do at Jane Street possible. signalsandthreads.com/the-thermody...

I had a lot of fun giving this talk in Singapore about the many-years-long saga of multicore OCaml, and in particular, the work over the least 2.5 years of getting it ready for production work within Jane Street's walls. www.youtube.com/watch?v=XGGS...

My approach so far is to treat AI code assistants as an extension of “a large team with communication challenges working on the same codebase.” You need better tools to clean up the local optima that individual agents get stuck in. See prune and merlint: discuss.ocaml.org/t/ann-new-to...

Yet another small OCaml/OxCaml diff has been squished! Polymorphic parameters has just gotten merged upstream: github.com/ocaml/ocaml/... There's more to go (include functor, for example: github.com/ocaml/RFCs/p...), but it's nice to see more progress in this space.

We're starting to think about how to evolve OCaml to be a more effective language for agentic programming. One intuition here is that agents change what's important in 2 ways: - the toil of writing matters less - the ease of understanding and verifying matters more 🧵1/3

We're starting to think about how to evolve OCaml to be a more effective language for agentic programming. One intuition here is that agents change what's important in 2 ways: - the toil of writing matters less - the ease of understanding and verifying matters more 🧵1/3

Some fun OCaml GC projects here with @sadiq.toao.com and @kcsrk.info if any students are looking for projects involving programming languages toao.com/blog/ocaml-0...

PSA! Please share around! Due to a limited number of submissions, we're extending the OCaml Workshop deadline by a week to July 10th AoE! Functional programmers! Heed my call! We need your submissions!!

A gem from Stephen Dolan, which proposes replacing the "generational hypothesis" that drives the design of generational GCs with a notion of lifetime dispersion as measured by the gini coefficient. Nice to see economics playing a role here! dl.acm.org/doi/pdf/10.1...

Something I predict will happen soon is using LLMs to port large test suites from one language / framework to another. Imagine starting a graphics or networking project and having hundreds of thousands of test cases already implemented!

taking a go at oxcaml today first attempt: let's try a parallel reduction. Idea is to compute the "sum" of [f(lo), ..., f(hi-1)] in parallel, combining via some associative function g (and corresponding zero element, z).

Over the 10 days, I wrote a new Racket library for "expect testing", a style that @yminsky.bsky.social has advocated for in OCaml. github.com/samth/recspe... As an experiment, I built it entirely with Codex (the OpenAI async AI programming tool). I have some thoughts.

A thing that people may not realize is how new some of the OxCaml extensions are. We are on the verge of rolling our very first data race free parallel program into production. Almost no one at Jane Street knows how to use this stuff yet!

The memory management aside, I’m really excited about the stuff already in the process of being upstreamed, like labelled tuples, polymorphic parameters and include functor. Those will be really handy to have!

OxCaml SIMD primitives are looking really nice 👀 > [unboxed vector values] are passed between functions in XMM registers, stored in structures as flat data, … > Within a function, all SIMD vectors live in floating-point registers or 16-byte aligned stack slots. oxcaml.org/documentatio...

And here's a blog post, announcing the release! blog.janestreet.com/introducing-...

I'm pleased to announce OxCaml! OxCaml is Jane Street's branch of OCaml. We've given it a new name and a snazzy logo, and done a bunch of work to make it easy for people to try.

Fun talk preparation trick: use Claude Code to create HTML animations for complex diagrams I want. Talk it through, explain in English, maybe even share a snapshot of a hand-draw diagram to get it going. It takes some babysitting, but the results are better than what I would have gotten on my own.

I was recently reminded of this old post, highlighting how broken IEEE NaNs are. Really, ML and its descendents had the right idea here, and everything else is kinda broken. blog.janestreet.com/making-somet...

Using uniqueness mode for improving behavioural types: kcsrk.info/ocaml/modes/...

A new Signals and Threads just dropped, with @ianthehenry.bsky.social! This one is about building tools for traders, but it also has some fun dives into Ian's personal projects, including bauble.studio and janet.guide. Anyway, more here: signalsandthreads.com/building-too...

I'm curious if anyone could summarize for me the state of evidence on the utility of type systems in reducing software faults. I'm aware of and even the source of some of the anecdotal evidence, but I'm curious if there's anything even vaguely methodologically rigorous.

Wild stuff.

The other great thing about AI-assisted programming in OCaml is expect tests. They give you a great way of making the behavior of your program visible, both to you, and to the AI. It provides a valuable feedback loop that the AI can leverage in all sorts of flexible ways.