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Jane Street Open Source

opensource.janestreet.com

64 points_benj22 comments

Lists don't make great HN submissions, because the topic is then the common denominator of the things on the list, making discussion generic and therefore more shallow.

It's usually best to pick the most interesting item on the list and submit that instead!

https://hn.algolia.com/?dateRange=all&page=0&prefix=true&que...

Good to know. Thanks!

(Both the company and the projects are very impressive of course! Not to mention OCaml itself.)

All hail the gods of OCaml.

As far as I can tell Jane Street's use of OCaml serves a dual function in talent acquisition and retention.

1. You attract the kind of Haskell adjacent academic talent who proves their natural curiosity by their interest in pure functional languages.

2. You are the only game in town for your newly created OCaml experts. Monopsony power baby!

Do they need to use a functional language? Almost certainly no.

I think this was the speech 15 years ago when they were just starting. I suspect OCaml isn't relevant in their recruitment strategy, apart from specialized profiles.

Jane Street leadership have said that programming languages matter. I think they just really believe in FP.

Years ago when I was more active in the OCaml community there were lots of talks of Jane Street programmers (including those who first introduced OCaml there) about why they specifically chose OCaml.

FP provide type system that are really hard to emulate in other languages. Static type interference is easy to use and at the same time extremely powerful. Static type interference with algebraic types is even more powerful.

In addition OCaml has an absolutely pedantic type system. While ints may be implicetly coerced to a double in other languages, this kind of conversion will be rejected by the OCaml compiler.

Since Jane Street uses their code on the stock market for trading, they don't want to have tests showing their code is correct, they want definite proof. And OCaml can in fact provide that. If you write the libraries correctly, the compiler will prove the correctness of the code.

At the same time OCaml isn't as pedantic about coding paradigms as e.g. Haskell, allowing imperative and object oriented code as well. You could do similar proofs in Haskell but a lot of stuff is much harder to do in a language that is pure FP and not multiparadigm.

I knew OCaml was being used by a number of big finance companies, or that it had been used. I really didn't know it was still active. Has anybody here used it? How was it?

Sure, but Jane Street, as mentioned here, is probably the largest user of it that I'm aware of. It is a great language, but F# is the more pragmatic choice these days. OCaml doesn't have a huge ecosystem where as F# inherits all the .NET libraries.

Most ordinary shops are just better off avoiding these stacks altogether. They don't really all that much compared to your C based languages. And its pointless to keep your hiring pool small.

There is also a steep learning and onboarding curve to climb when you onboard new employees. Significantly low help when you face issues, and just overall lack of help and information when you are stuck in a non-trivial issue. This is not just with F# or OCaml, but with all non-C based languages.

Only reason hedge funds can continue using this is they can pay people to suffer through this.

Some years ago I migrated from OCaml to Rust, I think it was the right decision.

I've barely touched OCaml but having worked professionally in Haskell for a few years I thought that OCaml was terrible. However, Jane Street has invested heavily in it and maybe their codebase is better than the glimpse I got of the language.

I've dipped my toes into machine-readable mathematical proofs. The theorem proving software called Coq [1] is written in OCaml.

[1] https://en.wikipedia.org/wiki/Coq_(software)

How does one get in Jane Street? They do fascinating stuff.

There has always been a mystery around it since back in my college days.

Apply, like anywhere else. Most quant firms expect you to be pretty strong with C++, but since they use OCaml (and don't expect you to know that) I think you can get away with low-level systems experience more broadly.

Speaking broadly about not only Jane street, but adjacent firms like Jump and Citadel: In my experience (working with and getting coached by a recruiter in the space), these finance companies really want you to love the space, not just the technology. I wasn't able to drink the kool-aid or fake enough die-hard passion for trading to get far in the their interview process, despite having extremely relevant technical capabilities Some are also very elitist with respect to your pedigree, so even amazing experience but no degree from a top US school can make it difficult (yes, even a decade later..)

> top US school

top schools outside of the US work too...

No direct experience but I would imagine you would need solid intermediate skills at OCaml, probably being a nerd enough to make your own extensions or the ecosystem for benchmarking and debugging, not just coding. Then a liberal dose of projects about OCaml, game theory, and financial markets. That ought to get their attention at least.

What I've heard is that they target graduates from elite schools, bonus points if you did maths or CS competitively. Everything else, including OCaml and finance, they claim that they can teach you. Although they always go to functional programing conferences like ICFP to promote their company, so they must hire language experts as well.

I applied there 15 years ago. They asked me some logic puzzles and some typical quant interview probability questions. It wasn't about OCaml at all even though I do have an OCaml background and I thought I interviewed for a SWE position. I remember the interviewer was unpleasant for no reason.

A friend of mine interviewed there recently, he got some typical leetcode questions (hard ones).

Some great additions lately to open source from some very successful institutions. I hope that the "Open" public benefit corporations decide to follow in the footsteps of their poorer peers, the hedge fund managers, and giving a little something back.

It was a while ago but Bloomberg FOSSed ComDB which was cool of them:

https://bloomberg.github.io/comdb2/overview_home.html

How does this compare to mysql and postgres?

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