O(x)Caml in Space

Well, I might have been the first to put OCaml in space, specifically on low-Earth orbit aboard GHGSat-D in 2016. I designed the payload software as a collection of SystemD services talking over DBus, and it included a CCSDS-to-DBus bridge to talk to the platform (the thing that hosts the payload, controls and steers the satellite). The payload also did perform symmetric-key encryption of the resulting data, as per regulations.

I gave a talk about the payload software at the Paris OCaml users group.

The reason for selecting that archicture was that I didn't expect to write the whole payload software by myself, and I assumed that when some other developers join in they would, obviously, not want to use a weird language like OCaml, and so they could write their portion in C/C++/whatever and the system could still work. Of course that didn't happen.

I'd be surprised if the company still uses OCaml, as the standad tendency is to revert to "industry-standard" languages to get industry-standard problems. The whole processing and simulation toolchain was also written in OCaml.

Today there is little reason not to use Rust and it can cover both the processing side and the payload software. But people still insist on using C/C++. I'm OK with that as long as I can invoice them.

EDIT: Found my slides https://lambda-diode.com/static/data/GHGSat_OCaml.pdf

I've long thought that Rust needs a similar algebraic effects system to OCaml 5, has anyone used both and compared how well they work for various use cases? Rust is of course more mature than OxCaml but if it's good enough for Jane Street...

The big win here is having a GC by default, with the ability to reduce heap allocations (via stack) just by adding in more typing annotations.

    Switching to OxCaml with exclave_ stack_ annotations drops 
    p99.9 latency from 29 ns to 9 ns per packet on the dispatch
    hot path, and removes GC pressure entirely (394 minor GCs to
    zero over 25 million packets). Throughput is comparable [...]

I got a similar result with my 'httpz' stack a few months ago (https://anil.recoil.org/notes/oxcaml-httpz) which my website's been running on without drama. And, I gotta say, OxCaml's a surprisingly robust compiler for being packed full of bleeding edge extensions: not a single crash on my infra is attributable to a compiler bug (plenty of bad OCaml code, but not due to a compilation bug)

I know that many garbage collected languages have ways of reducing gc pressure by minimizing classes, and pushing more things on the stack. I’ve even heard how languages like Java will allocate a massive amount of memory in the beginning, and then turn. Off the garbage collector for the whole day in high frequency trading scenarios.

Having never been in this situation, I wonder how difficult it is to bend a garbage collected language to behave like a non garbage collected one

What’s surprised me in the last few months is that agents are great at producing OCaml 5+ and OxCaml code, not much of which is out there in the training data. OxCaml’s strong types and modes seem to serve as great testable oracles to guide the agents.

I taught a course on concurrent programming based on OCaml 5 and OxCaml where almost all of the code in the teaching materials were vibe coded. I reviewed all of the code (because I was teaching it to a class of 50+ students) and frankly the agent writes better O(x)Caml (mostly) than me.

CCSDS guides you to reinvent everything from scratch, I doubt memory safety is the biggest attack surface when you implement this stack. I dont know how big players implement networking for their satellites, but personally I would choose to fit something existing and battle-tested like TLS instead of reinventing data encryption, just look at those documents: https://www.google.com/search?client=firefox-b-lm&q=ccsds+en...

HN is currently obsessed with Rust vs Zig. OxCaml should be considered as an alternative to both. The argument for Rust is safety, while for Zig it's ergonomics, but OxCaml shows you can have safety and ergonomics together. In my little tinkering with it [1] I found it really easy to use.

[1]: https://noelwelsh.com/posts/a-quick-introduction-to-oxcaml/

>KC ended his talk speculating that OCaml 5.0 would go to the moon, due to its language features that would deliver C/Rust-like performance

That is quite an affirmation! I would likle to see OCaml being there.

nice

nice

She (Jane Street) is not gonna notice you bro.