OCaml Weekly News

Previous Week Up Next Week

Hello

Here is the latest OCaml Weekly News, for the week of July 15 to 22, 2025.

Table of Contents

Third outreachy internship blog

Archive: https://discuss.ocaml.org/t/third-outreachy-internship-blog/16984/1

Matthew Idungafa announced

Hello everyone, it's the mid-point of my oureachy internship with Dune and here's my third blog post

In this article, I talk a bit more about the ocaml ecosystem in general and offer some insights to devs who would want to contribute to the ocaml ecosytem in subsequent internships.

opam 2.4.0 is out!

Archive: https://discuss.ocaml.org/t/ann-opam-2-4-0-is-out/16989/1

Kate announced

Hi everyone,

We are extremely happy to announce the release of opam 2.4.0 and encourage all users to upgrade.

What’s new? Some highlights:

  • :dragon_face: On opam init the compiler chosen for the default switch will no longer be ocaml-system (#3509) This was done because the system compiler (as-is your ocaml installed system wide, e.g. /usr/bin/ocaml) is known to be under-tested and prone to a variety of bugs and configuration issues. Removing it from the default compiler allows new-comers a more smooth experience. Note: if you wish to use it anyway, you are always able to do it explicitly using opam init --compiler=ocaml-system
  • :dragon: In the same vein, opam switch create [name] <version> will not include compiler packages flagged with avoid-version / deprecated in the generated invariant anymore, unless compiler flagged avoid-version / deprecated are the only ones available (#6494) Note: if you wish to use ocaml-system, you can simply say it explicitly using opam switch create [name] ocaml-system
  • :yarn: opam install --deps-only no longer requires unicity of package version between the request and the installed packages. In other words, if you have pkg.1 installed, installing the dependencies of pkg.2 no longer removes pkg.1 if the installed packages are compatible. This also allows to install dependencies of conflicting packages when their dependencies are compliant. (#6520)
  • :camel: GNU patch and the diff command are no longer runtime dependencies. Instead the OCaml patch library is used (#6019, #6052, #3782, ocaml/setup-ocaml#933) Doing this we've removed some rarely used features of GNU Patch such as the support of Context diffs. The new implementation only supports Unified diffs including the git extended headers, however file permission changes via said extended headers have no effect.
  • :snowflake: Add Nix support for external dependencies (depexts) by adding support for stateless package managers (#5982). Thanks to @RyanGibb for this contribution
  • :cockroach: Fix opam install <local_dir> with and without options like --deps-only or --show-action having unexpected behaviours (#6248, #5567) such as:
    • reporting Nothing to do despite dependencies or package not being up-to-date
    • asking to install the wrong dependencies
  • :window: The prebuilt Windows binary now includes Cygwin's setup-x86_64.exe in the binary itself as fallback in case cygwin.com is inaccessible (#6538). Opam will also no longer fail if cygwin.com is inaccessible when checking for upgrades of setup-x86_64.exe (#6495, #6474)
  • :ocean: Many more UI additions and improvements, bug fixes, …

:open_book: You can read our blog post for the full list of important changes, and for even more details you can take a look at the release note or the changelog.

Try it!

The upgrade instructions are unchanged:

For Unix systems 

bash -c "sh <(curl -fsSL https://opam.ocaml.org/install.sh) --version 2.4.0"

or from PowerShell for Windows systems 

Invoke-Expression "& { $(Invoke-RestMethod https://opam.ocaml.org/install.ps1) } -Version 2.4.0"

Please report any issues to the bug-tracker.

Happy hacking, <> <> The opam team <> <> :camel:

I'd also like to personally give a special thanks to the whole haematology department of the NHS Greater Glasgow for making my continued existence and this release – in the state that it is – possible. Fighting cancer is not easy but it is much more bearable with great people <3

Kate later added

[NOTE] We have had reports of a regression in some cases when using pin-depends. We have a fix and we're planning to have 2.4.1 out in a couple days.

x-ocaml, notebooks as a webcomponent

Archive: https://discuss.ocaml.org/t/ann-x-ocaml-notebooks-as-a-webcomponent/16996/1

art-w announced

Dear internets,

I would like to share x-ocaml, a little project to make it easier to share executable OCaml examples on the web. To enable readers to experiment with the code, x-ocaml integrates the CodeMirror editor with the js_of_ocaml-toplevel interpreter, Merlin and OCamlformat. You only need to add the following in your html page to use it: 

<script async
  src="https://cdn.jsdelivr.net/gh/art-w/x-ocaml.js@5/x-ocaml.js"
  src-worker="https://cdn.jsdelivr.net/gh/art-w/x-ocaml.js@5/x-ocaml.worker+effects.js"
></script>

This script will introduce a new HTML tag <x-ocaml> to present your OCaml code: 

<x-ocaml>let it = "be"</x-ocaml>

The online demo shows a couple more examples and configuration options. In particular, there is a command-line tool in the github repo to export OCaml libraries and load them into your page: 

$ x-ocaml --effects digestif.ocaml -o digestif.js
# then use <script async src="..." src-worker="..." src-load="digestif.js">

I believe this could be very useful in tutorials or documentation to showcase your favorite OCaml libraries.

While searching how to implement this, I discovered sketch.sh which had so many good ideas and that we should use a lot more! My hope is that x-ocaml can provide a similar notebook experience for the rest of the web, by being easy to integrate in static webpages.

Besides the js_of_ocaml authors and the many OCaml playgrounds that have inspired this project, I would like to address some special thanks to:

  • @patricoferris for the jsoo-code-mirror bindings, and for the xocmd tool to convert markdown files to use <x-ocaml> tags
  • @vds for integrating Merlin with javascript and CodeMirror in merlin-js
  • @juloo for his assistance on the ocamlformat support
  • @kayceesrk for reporting issues and requesting features which have made the tool a lot more robust and versatile! His blogpost "Testing x-ocaml, OCaml notebooks as a WebComponent" also provides a longer example of what can be done with it (and the limitations you might run into)

Dune dev meeting

Archive: https://discuss.ocaml.org/t/ann-dune-dev-meeting/14994/33

Puneeth Chaganti announced

Hi everyone! :camel:

We will hold our regular Dune dev meeting on Wednesday, July, 23 at 9:00 CET. As usual, the session will be one hour long.

Whether you are a maintainer, a regular contributor, a new joiner or just curious, you are welcome to join: these discussions are open! The goal of these meetings is to provide a place to discuss the ongoing work together and synchronize between the Dune developers :smile:

:calendar: Agenda

The agenda is available on the meeting dedicated page. Feel free to ask if you want to add more items in it.

:computer: Links

Lwt.6.0.0~alpha (direct-style)

Archive: https://discuss.ocaml.org/t/ann-lwt-6-0-0-alpha-direct-style/16972/26

Deep in this thread, Raphaël Proust announced

version 6.0.0~alpha01 is now ready (https://github.com/ocaml/opam-repository/pull/28222)

Anyone able to test the release on their existing code, I'd welcome the feedback: does it work? There shouldn't be breakages but then there might. If you are not sure how to test or what to test, don't hesitate to ask (on here or via dm or via discord).

Other OCaml News

Old CWN

If you happen to miss a CWN, you can send me a message and I'll mail it to you, or go take a look at the archive or the RSS feed of the archives.

If you also wish to receive it every week by mail, you may subscribe to the caml-list.