> And because Bonsai is written in OCaml, it becomes possible to use the same language and types on both the backend and frontend.
Finally! I was waiting for this to become possible!
deciduously 5 hours ago [-]
There's also Fable for F# but I believe this commenter is being sarcastic. Javascript is a common backend language.
5 hours ago [-]
rhgraysonii 3 hours ago [-]
A really great place to reach for this is Elixir/Phoenix now that the set theoretic type system is in place with LiveView. I have been doing some pretty large/complex codebases gradually working towards fully integrating working this way for the past 5 years and it has been great.
philipwhiuk 7 hours ago [-]
Similar attempts include Scalajs.
The general challenge becomes integrating the fractional front-end code written in your backend-language that compiles to JS with the rest of the JS ecosystem.
JaneStreet have a love of writing their own stuff from scratch so it doesn't apply to them but it might to you.
Hence most people end up with frontend-as-backend rather than backend-as-frontend.
vips7L 2 hours ago [-]
KotlinJs and ClojureJs too. You always end up having to write wrappers or dealing with problems that would just work if you just used normal js/ts.
lbourdages 7 hours ago [-]
Couldn't WASM solve that problem once and for all? Is there some limitation that WASM has that JS doesn't?
Disclaimer: I am very inexperienced at front-end development.
danielheath 6 hours ago [-]
> Is there some limitation that WASM has that JS doesn't?
You need a JS trampoline to call your WASM and make browser primitives available to it, and IIRC calls into browser code incur some extra overhead, but those are pretty manageable.
Additionally: for high level languages, source code is _much_ smaller than compiled binaries. If your initial needs are simple, your users are likely downloading more than 10x as much code.
applfanboysbgon 5 hours ago [-]
WASM does not (yet) have access to the DOM or web APIs, meaning every direct interaction with the browser must first go through JS interop anyways, with a resulting performance penalty. There are proposals, and maybe we'll see it happen by 2035, but as of now WASM is best suited for heavier workloads where the edge in application performance outweighs the cost of JS interop with the browser rather than being a universal solution.
A framing from that podcast that helped me better understand the role of Bonsai is that it's really a framework for building incremental distributed state machines.
dtornabene 2 minutes ago [-]
The docs are a bit sparing but if you read the source its pretty cool to see how they did this.
frutiger 53 minutes ago [-]
This framing is also in the post. From the readme:
> Bonsai itself -- this library -- is actually more generic than the above makes it sound. It allows you to build general-purpose incremental, composable state machines. Bonsai_web builds on top of that core library, specializing it for interactive browser-based UIs, but we also have Bonsai_term for building interactive terminal-based UIs.
rw2 6 hours ago [-]
I am sure it's very performant, but to me it's extremely ugly; Surely someone can fix margins and still have it be performant.
pgwhalen 6 hours ago [-]
I’m no UI expert - what’s wrong with the margins?
LooseEquipment 6 hours ago [-]
inconsistent and maybe too tight, but I would think those are issues with the sample UIs and not this library
OneDeuxTriSeiGo 5 hours ago [-]
FWIW if you listen to Signals and Threads (the Jane Street podcast) they talk about this.
They have dedicated UX designers who do relatively little code but focus entirely on making the UX as optimal for the traders as possible and one of them was on an episode.
They talked about how most of the normal UX rules for SW go out the window because quants and traders have such different needs than "normal software".
chrisweekly 3 hours ago [-]
This matters. Beyond performance (a universal good), the definition of "good" UX is strictly dependent on the user. Fintech platforms for traders who open a multi-window thick client application(s) and spend hours in it every day have little in common with consumer mobile apps designed to hold your attention for maybe a minute. It's mind-bogglingly lazy to choose something like MUI (Material UI) as if it were some kind of reasonable foundation irrespective of context.
jackcarter 5 hours ago [-]
Is there any professional software that wouldn't benefit from high information density? Most software design is optimized for the non-users who have to approve it.
jacobolus 7 minutes ago [-]
You can have high information density and still not have words running into each-other. Taking all of the space out from around text and information graphics makes them less legible, even for experienced "power users".
I think the goal here is more an aesthetic of being for "serious traders only" rather than a UI optimized for speed and clarity.
ambicapter 4 hours ago [-]
"non-users" are also big targets for software. If you run a software business, chances are you want people who've never used your software to start using your software. In that case, discoverability trumps high information density.
tjoff 2 hours ago [-]
It only adds discoverability for the things that fit the screen. In other words, you have to make it simple. I.e. the lazy way to make something "user-friendly", do as little as possible and force the user to adapt to your ways instead.
RugnirViking 3 hours ago [-]
this - most of the internal software at my job that's actually important is very dense, with keyboard navigation and shortcuts. The ones that somebody makes to sell themselves to upper management while angling for a promotion look very pretty, and never get used.
And yet, we make such beautiful and vacant software ourselves for our clients, because again, its b2b, so you aren't selling to the people who actually have to use the software. Im glad at least we arent forced that often to use specific internal tools, the better ones just get adopted organically
dmoy 23 minutes ago [-]
Fair point
I guess JS doesn't have to care about this at all because they're not selling their UI to others, just making it in house for in house use
pgwhalen 5 hours ago [-]
From experience I can say that traders prefer extraordinarily little whitespace in their UIs.
stronglikedan 51 minutes ago [-]
Margins on an info dashboard are wasted space.
troupo 5 hours ago [-]
I'd kill for tight UIs now. Everything insists on having 15000-mile wide margins, and at most two items visible on an 8K screen.
We are at a point when TUIs from 1990s running in 12" screens with at best a 480x240 resolution display more info than almost anything we have now.
ctxc 5 hours ago [-]
Probably because they skew towards higher information density
4 hours ago [-]
chrischen 7 hours ago [-]
Curious how this compares to Melange which is used by Ocaml shops as well to double up on Ocaml for both front and backend (ahrefs being the major user and sponsor). Does this mean giving up a lot of the JS ecosystem (React, graphql, etc)?
user2342 5 hours ago [-]
Interesting! What are Bonsai's dependencies? I use OCaml but - so far - none of Janestreets libraries etc.
LeonidasXIV 4 hours ago [-]
Basically most of Jane Street's published code[0] via its dependency on Core.
What does JaneStreet do besides sponsoring nerdy Youtube channels and writing UI libraries?
markoman 13 minutes ago [-]
Jane Street made it's way into today's Wall St Journal for its quantitative prowess and hiring of Math PhD's. What was stunning to hear was that their 2nd quarter profits were a record $10.3 billion, nearly double that of Goldman Sachs and Morgan Stanley (much larger firms).
RugnirViking 3 hours ago [-]
They're a trading firm that hires really clever people to use math to trade. Their strategies are, presumably, very complicated and ever changing, and secrecy about them is the point - you get bigger margins for longer if people don't learn about your 'one weird trick' (that and also that there is presumably another side to your trades losing out on upside, and they might not be best pleased to learn about it.
rudedogg 3 hours ago [-]
> really clever people
Sam Bankman-Fried and his League of Legend rankings would like a word
affyboi 42 minutes ago [-]
They’re a market maker
morkalork 4 hours ago [-]
Print money?
andor 2 hours ago [-]
Governments print money, high frequency traders extract money. They would say that they provide liquidity to the market as a service.
morkalork 1 hours ago [-]
hn: come for the tech news, stay for the pedantry
phplovesong 4 hours ago [-]
Market manipulation. They got kicked out and banned from the asian markets for fraud.
EDIT.
Janestreet PR team is downvoting. Like always, radio silence and just downvotes.
I had expected more from janestreet.
monooso 2 hours ago [-]
This doesn't seem quite as clear-cut as you're making out.
The Securities and Exchange Board of India (SEBI) have accused Jane Street (JS) of market manipulation, JS claims it was legitimate arbitrage, and the case is still ongoing [1].
As I understand it, the ban only applied to Indian securities (not Asian markets as a whole), and was lifted back in July 2025 after JS paid ~$560 million (the alleged ill-gotten gains) into an escrow fund. They don't appear to have resumed trading, though [2].
The above might be too far-fetched as it only applied to India? They did pay a fine to the regulator and resumed trading (might not be the same strategy though)
To OP’s original question, they made $20B last year and have a niche in several financial products
phplovesong 3 hours ago [-]
Yes, the fraud was done in india. Why does that matter?
fn-mote 22 minutes ago [-]
“Banned from the Asian markets” was the original claim. The actual fact is: banned from Indian markets, with the ban now lifted.
wbl 2 hours ago [-]
Trading the underlying to offset your derivative position isn't fraud.
vovavili 2 hours ago [-]
>Janestreet PR team is downvoting. Like always, radio silence and just downvotes.
You're being downvoted for having a needlessly confrontational underinformed hot take on a quant trading firm that is essentially a market maker.
Schlagbohrer 6 hours ago [-]
Can someone who understands web UI programming tell me if this would be good for my local agent to use to produce HTML based reports and outputs for me? Or for TUI outputs?
tikhonj 3 hours ago [-]
The main thing that Bonsai gets you is a nice programming model for making your UIs interactive. If you're mostly producing static reports (with maybe some basic interactive visualization widgets or something), it will not get you much over generating some variant on HTML + JS.
It makes more sense for applications where you have complex interactive logic in the UI, with a lot of different components that need to control and display some shared state.
derdi 5 hours ago [-]
There was this submission two months ago: https://news.ycombinator.com/item?id=48365904 . Basically they have a TUI frontend for the same thing. And the blog post says: "Bonsai_term would feel familiar to anyone who’d ever done web development here, and it had the huge advantage of being especially amenable to AI assistance. It was actually somewhat of a mystery to us how good the models were at writing Bonsai_term code, given how relatively obscure it is [...]"
antonvs 5 hours ago [-]
Probably not, because your agent won’t have much info about this tool in its training set.
xvilka 9 hours ago [-]
Looks like it's Web-only, no mention of the native UI support (terminal UI excluded).
avsm 8 hours ago [-]
There's a full terminal implementation of Bonsai as well. I actually use it in my personal workflow these days to manage my contacts database! https://anil.recoil.org/notes/aoah-2025-9
abtinf 3 hours ago [-]
Seconding the sibling comment - what are you using to run your personal site? It is very nice.
aquariusDue 7 hours ago [-]
Unrelated but what do you use to manage your personal website? I love how everything is interconnected.
avsm 3 hours ago [-]
Custom infrastructure; I use my site as a playground for various things over the years. It ran as the first MirageOS unikernel for many years, and recently it's been running on a zero-allocation OxCaml webserver https://anil.recoil.org/notes/oxcaml-httpz to help me get to grips with the new extensions.
ubercore 7 hours ago [-]
Not sure why, but reminds me of Fog Creek's Wasabi.
simonask 5 hours ago [-]
I really want to like OCaml. One day I'll get around to learning it.
hahahaa 9 hours ago [-]
Oh it needs a userland trampoline!
> JSOO does not have tail call optimization
debugnik 3 hours ago [-]
Jsoo supports self-recursive and mutually recursive tail calls, but for general tail calls it would need to trampoline every single call, since the only major browser with proper tail calls is Safari.
adastra22 7 hours ago [-]
The “The thinking in bonsai” link 404s.
This says it is based on Elm. So it has the same clean immutable state structure?
kubb 8 hours ago [-]
I wish there were more OCaml shops out there
Onavo 2 hours ago [-]
Considering how ridiculously verbose their library is compared to React/Vue it's a good thing we have LLMs to deal with the boilerplate now.
MrBuddyCasino 6 hours ago [-]
This is great. It focuses on utility and information density over design. It looks like someone took a terminal UI and transplanted it to the web, Bloomberg terminal style.
I'm pretty sure you can build tools with this that are fast and pleasant to use.
bobjansen 8 hours ago [-]
This would of been cool back in 2014.
_flux 3 hours ago [-]
Ocsigen and Eliom were started 2005 and are pretty similar, although I can't find any well-known projects using Eliom :/.
Presumably this has learned some lessons from it, so it's probably better.
Traster 9 hours ago [-]
The "Why Bonsai?" I found really funny.
Let me re-write that section for you:
Why Bonsai?
At Jane Street we're super excited by Functional programming and by CAML in particular, so when we need low latency software, we use OCAML, when we need hardware, we write out own langauge - HardCAML, and when we need a Web UI, we build a Web UI framework in CAML. Because we fucking love CAML.
troupo 6 hours ago [-]
And there's nothing wrong with that. Many languages attempt to do the same thing. Why bother with 15 different languages if you can leverage one?
See also LiveView and Hologram for Elixir.
bofeiw 8 hours ago [-]
Agreed, looks like it's reinventing the wheels. Frameworks does not really matter today, AI agents write the code anyway.
KolmogorovComp 8 hours ago [-]
But AI do benefit a lot from a strict compiler, and having a simple language improve a lot on type-safety, so I don't think it is to throw, even today.
rmzs0711 8 hours ago [-]
But what about compilation speed? Hot reload? Maintainability? What is the bus factor for these kind of technologies?
Yea, its cool to have strict type safety, but what's the point of it doesn't have all the benefits from other Frameworks that took years to polish
OtherShrezzing 7 hours ago [-]
JaneStreet has enough free cash to not worry about those issues. If one of their key persons dies in service, they can go out and contract the worlds leading expert in that domain, and their annualised rate isn’t even a rounding error on their bottom line.
zem 1 hours ago [-]
ocaml has excellent compilation speed, and in my experience the code is very maintainable due to the module and type systems.
shAIster 7 hours ago [-]
AI certainly writes Internet comments so that the flock does not have a single minute to get independent thoughts.
ForHackernews 8 hours ago [-]
Better frameworks will still help AIs avoid silly mistakes. A smarter framework means you can be productive with a dumber/cheaper AI.
nbevans 7 hours ago [-]
It looks like a nice little library; but oh boy must this be so limiting for the product teams that are forced to use. Everything looks like it's straight out of the 1990s.
gigatexal 7 hours ago [-]
All your money and retirement funds are safe; I’m too dumb to work at JaneStreet; every time I see OCAML I feel less than and confused.
phplovesong 4 hours ago [-]
Related:
Janestreet was banned from asian markets for market manipulation. They took in billions and fisted the average-joe investor. As a high profile ocaml user that casts a big shadow on ocaml too, as many involved in janestreet are also part of ocaml core team in some way.
I wont buy ignorance, as devs clearly know whats going on, so staying silent is pretty much being just as guilty.
Paradigma11 3 hours ago [-]
If you read up on it that was basically India protecting its corrupt cronies. Janestreet showed severe problems with some Indian companies and instead of fixing that and creating a healthier and more transparent market they decided to go after the messenger.
tecoholic 6 hours ago [-]
Why does this library get posted here, what feels like every month? I remember it seeing at least twice before.
cassepipe 5 hours ago [-]
Been here 5 years, never saw it
jere 6 hours ago [-]
HN is obsessed with anything done in niche programming languages, is my guess.
bmitc 6 hours ago [-]
Also, Jane Street.
yuanBuilds 5 hours ago [-]
It might be a very performant UI framework in OCaml, but all the UI elements look extremely unpolished to me, like what a really smart high-school kid would build the GUI for his side project on Windows in 90s.
Thanks, I can use JS as a functional programming language.
Rendered at 18:17:25 GMT+0000 (Coordinated Universal Time) with Vercel.
Finally! I was waiting for this to become possible!
The general challenge becomes integrating the fractional front-end code written in your backend-language that compiles to JS with the rest of the JS ecosystem.
JaneStreet have a love of writing their own stuff from scratch so it doesn't apply to them but it might to you.
Hence most people end up with frontend-as-backend rather than backend-as-frontend.
Disclaimer: I am very inexperienced at front-end development.
You need a JS trampoline to call your WASM and make browser primitives available to it, and IIRC calls into browser code incur some extra overhead, but those are pretty manageable.
Additionally: for high level languages, source code is _much_ smaller than compiled binaries. If your initial needs are simple, your users are likely downloading more than 10x as much code.
https://ocsigen.org/ in Ocaml too
https://websharper.com/ for fsharp and csharp. Really good when I used in in fsharp
Maybe https://melange.re/v7.0.1/ too? (Not sure)
Sarcasm?
Do you want to have a talk as to why JaneStreet wasn't built on JavaScript?
> Bonsai itself -- this library -- is actually more generic than the above makes it sound. It allows you to build general-purpose incremental, composable state machines. Bonsai_web builds on top of that core library, specializing it for interactive browser-based UIs, but we also have Bonsai_term for building interactive terminal-based UIs.
They have dedicated UX designers who do relatively little code but focus entirely on making the UX as optimal for the traders as possible and one of them was on an episode.
They talked about how most of the normal UX rules for SW go out the window because quants and traders have such different needs than "normal software".
I think the goal here is more an aesthetic of being for "serious traders only" rather than a UI optimized for speed and clarity.
And yet, we make such beautiful and vacant software ourselves for our clients, because again, its b2b, so you aren't selling to the people who actually have to use the software. Im glad at least we arent forced that often to use specific internal tools, the better ones just get adopted organically
I guess JS doesn't have to care about this at all because they're not selling their UI to others, just making it in house for in house use
We are at a point when TUIs from 1990s running in 12" screens with at best a 480x240 resolution display more info than almost anything we have now.
[0]: https://github.com/janestreet/bonsai/blob/f31661450eb133fe89...
Sam Bankman-Fried and his League of Legend rankings would like a word
EDIT.
Janestreet PR team is downvoting. Like always, radio silence and just downvotes.
I had expected more from janestreet.
The Securities and Exchange Board of India (SEBI) have accused Jane Street (JS) of market manipulation, JS claims it was legitimate arbitrage, and the case is still ongoing [1].
As I understand it, the ban only applied to Indian securities (not Asian markets as a whole), and was lifted back in July 2025 after JS paid ~$560 million (the alleged ill-gotten gains) into an escrow fund. They don't appear to have resumed trading, though [2].
[1]: https://www.reuters.com/legal/government/us-trading-firm-jan...
[2]: https://www.reuters.com/sustainability/boards-policy-regulat...
To OP’s original question, they made $20B last year and have a niche in several financial products
You're being downvoted for having a needlessly confrontational underinformed hot take on a quant trading firm that is essentially a market maker.
It makes more sense for applications where you have complex interactive logic in the UI, with a lot of different components that need to control and display some shared state.
> JSOO does not have tail call optimization
This says it is based on Elm. So it has the same clean immutable state structure?
I'm pretty sure you can build tools with this that are fast and pleasant to use.
Presumably this has learned some lessons from it, so it's probably better.
Let me re-write that section for you:
Why Bonsai?
At Jane Street we're super excited by Functional programming and by CAML in particular, so when we need low latency software, we use OCAML, when we need hardware, we write out own langauge - HardCAML, and when we need a Web UI, we build a Web UI framework in CAML. Because we fucking love CAML.
See also LiveView and Hologram for Elixir.
Yea, its cool to have strict type safety, but what's the point of it doesn't have all the benefits from other Frameworks that took years to polish
Janestreet was banned from asian markets for market manipulation. They took in billions and fisted the average-joe investor. As a high profile ocaml user that casts a big shadow on ocaml too, as many involved in janestreet are also part of ocaml core team in some way.
I wont buy ignorance, as devs clearly know whats going on, so staying silent is pretty much being just as guilty.
Thanks, I can use JS as a functional programming language.