FUN OCaml is an open-source hacking event dedicated to OCaml enthusiasts and professionals alike. The second edition took place this year on September 15 and 16 in Warsaw, Poland, and LexiFi took part in it!
Thanks to the impeccable work of the organizers, a wonderful venue, great talks and plenty of goodwill, the event was a unalloyed success. Furthermore, the impressive stage and professional AV operators in charge of the event meant that the high-quality experience extended also to those attending remotely.
This year, LexiFi sponsored the conference, as part of its ongoing effort to give back to the OCaml community. In addition, we contributed a 30-minute talk and a 2-hour hands-on workshop.
The full live recording of all the talks is available below. Once the edited versions are ready, I will update the blog post with links (the individual videos will be made available at https://watch.ocaml.org, similar to what was done for the 2024 edition).
Talk: 25 years of OCaml at LexiFi
The 30-minute talk was a retrospective on LexiFi’s 25 years of working with OCaml to build and ship commercial software. After a short presentation of LexiFi and how it came to be, we covered many aspects of how OCaml is used and deployed in practice at LexiFi (you can scrub forward to 3:15:29 in the live stream to watch the video of the talk). Note that due to time limitations, the version of the slides below covers more ground than what is contained in the video.
Some issues touched upon in the presentation: the history of OCaml at LexiFi,
contributions and interaction with the upstream compiler and the OCaml
community, how we set up our development environment, build systems, use of
libraries, PPX, parallelism, language features used and avoided, debugging,
numerical code, CI, native Windows UIs (via csml, our .NET/OCaml bridge), JS
bindings via gen_js_api, hiring aspects, etc.
Towards the end, our “secret sauce” is discussed by way of examples. As is well-known, we maintain a fork of the official OCaml compiler extended with a form of type reflection. This technology is a key technical brick of how we develop software, and it certainly partly responsible for allowing us to be as productive as we are.
Workshop: adding type reflection to the compiler
Besides the 30-minute talk, we also contributed a hands-on 2-hour workshop. The subject of the workshop was our extension of the official compiler to support type reflection. The idea was to understand how the system works by implementing a toy version of it from scratch. It was the first time we tried something like this, but thanks in no small part to an enthusiastic audience, I walked away rather content with the experience.
The code that we wrote during the workshop is available in the repository below
(branch trunk).
https://github.com/LexiFi/fun-ocaml-2025
The slides for the workshop are below. Note that during the actual workshop we did not cover any of the extensions; we made it only as far as slide 20.
The video of the workshop has not yet been made available, but I will update the blog post once it is.
Questions? You can reach me at nicolas.ojeda.bar@lexifi.com. Happy hacking!