[Caml-list] Attn: Development Editor, Latest OCaml Weekly News

Alan Schmitt
2025-09-02T12:23:23Z

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Hello

Here is the latest OCaml Weekly News, for the week of August 26 to
September 02, 2025.

Table of Contents
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Porting my Toy OCaml Build System to Windows
mlfront-shell - reference implementation of a build system
An experimental branch of Merlin based on Domains and Effects
Ppx_rapper support, Caqti 2.0 port
Outreachy Demo Day August 2025
Other OCaml News
Old CWN

Porting my Toy OCaml Build System to Windows
════════════════════════════════════════════

Archive:
<https://discuss.ocaml.org/t/porting-my-toy-ocaml-build-system-to-windows/17185/1>

Steve Sherratt announced
────────────────────────

<https://www.gridbugs.org/porting-my-toy-ocaml-build-system-to-windows/>

mlfront-shell - reference implementation of a build system
══════════════════════════════════════════════════════════

Archive:
<https://discuss.ocaml.org/t/ann-mlfront-shell-reference-implementation-of-a-build-system/17186/1>

jbeckford announced
───────────────────

I’ve made a reference implementation (“mlfront-shell”) of a build
system that is mostly working but has zero (0) performance work so
far. Among the many existing build + package managers, the
“mlfront-shell” tool sits closest to Nix. It works on Windows, can
download binary assets, is language-neutral with an easy-to-parse JSON
build file.

The reference implementation comes with a specification doc and a JSON
schema. Since I’ll eventually be integrating the build system features
into `dk' (my OCaml scripting tool), the docs live there. You’ll find
a Quick Start guide and a Comparison table (the `opam' and `dune'
comparisons are pertinent):

<https://github.com/diskuv/dk/tree/1.0?tab=readme-ov-file>#

Huge thanks to the a la carte authors, and also to @hbr for
[fmlib_parse].

Aside: Wow, another Windows-friendly build system post at
<https://discuss.ocaml.org/t/porting-my-toy-ocaml-build-system-to-windows/17185>
!

Links:

• JSON schema for JSON build files: Follow the [Quick Start - Build
Tool] to see how to use it for auto-completion
• Specification:
<https://github.com/diskuv/dk/blob/1.0/docs/SPECIFICATION.md>
• <https://discuss.ocaml.org/t/ocaml-version-of-the-build-systems-a-la-carte-paper/17042>
topic
• Source Code: <https://gitlab.com/dkml/build-tools/MlFront> (in
particular the MlFront_Exec and MlFront_Thunk subprojects)

[fmlib_parse] <https://ocaml.org/p/fmlib_parse/latest>

[Quick Start - Build Tool]
<https://github.com/diskuv/dk/tree/1.0?tab=readme-ov-file#quick-start---build-tool>

An experimental branch of Merlin based on Domains and Effects
═════════════════════════════════════════════════════════════

Archive:
<https://discuss.ocaml.org/t/ann-an-experimental-branch-of-merlin-based-on-domains-and-effects/17195/1>

Xavier Van de Woestyne announced
────────────────────────────────

/The Merlin Team/ :man_mage: is very happy to announce an experimental
version of Merlin: [Merlin Domains]!

As a reminder, [Merlin] is an /editor service/ that provides advanced
IDE features for OCaml. It can be used as a standalone binary or as a
library, and is notably used by [OCaml LSP Server]. In other words, if
you are using the [OCaml Platform extension] with Visual Studio Code,
or [ocaml-eglot] with Emacs, you are already using Merlin *under the
hood*.

Even though over the years we’ve had relatively few complaints about
Merlin’s performance, in some contexts (notably very large /files/),
Merlin’s mechanism (`parsing file' (with recovery) -> `typing file'
(with recovery) -> `performing analysis') could sometimes cause
slowdowns!

To address these slowdowns, we started an experimental branch that
uses [domains] and [effects], which allow us *to interrupt the typing
process at the right moment* when an analysis request comes in.

In practice, let’s say you run an analysis command on a very large
file: *the type-checker will progress up to the location that makes
the analysis possible, run the analysis phase, return the result, and
then continue typing the file*. This separation is possible thanks to
control flow management enabled by effects, and by having two domains
interact with each other.

In practice, this makes the analysis phases much more efficient! We
think this is a great example of migrating a regular OCaml application
to one that takes advantage of multicore. For a more technical
explanation of *how this experimental branch works internally*, @pitag
and @Lyrm will talk about it at [Lambda World], in their talk [When
magic meets multicore - OCaml and its elegant era of parallelism].

Currently, the branch is still in its incubation phase, and *we’d be
delighted to get your feedback*!

[Merlin Domains] <https://github.com/ocaml/merlin/tree/merlin-domains>

[Merlin] <https://ocaml.github.io/merlin/>

[OCaml LSP Server] <https://github.com/ocaml/ocaml-lsp>

[OCaml Platform extension]
<https://marketplace.visualstudio.com/items?itemName=ocamllabs.ocaml-platform>

[ocaml-eglot] <https://github.com/tarides/ocaml-eglot>

[domains] <https://ocaml.org/manual/5.2/api/Domain.html>

[effects] <https://ocaml.org/manual/5.3/effects.html>

[Lambda World] <https://lambda.world/>

[When magic meets multicore - OCaml and its elegant era of parallelism]
<https://lambda.world/speakers/?speaker=Sonja%20Heinze>

How to test the branch
╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌

To avoid installing this version of `merlin' unintentionally, we
suggest /pinning/ this branch in the switches where you want to
experiment with this new version (compatible with Merlin’s `main'):

┌────
│ opam pin add https://github.com/ocaml/merlin#merlin-domains
└────

Although this experimental branch passes the /test-suite/, *your
feedback is very important* to help collect potential bugs we may have
missed. We’ve added a `Bug/Merlin-domains' label to organize tickets
related to this experimental branch.

Next steps
╌╌╌╌╌╌╌╌╌╌

In the future, the goal of this branch (which will be regularly
rebased on `main') is to *become the main branch*, so that all users
can benefit from these improvements. At the same time, the rest of
the ecosystem depending on Merlin (such as the *OCaml LSP Server*)
will be adapted to also take full advantage of these new features!

/Happy Hacking!/ The Merlin Team :man_mage:

Ppx_rapper support, Caqti 2.0 port
══════════════════════════════════

Archive:
<https://discuss.ocaml.org/t/ppx-rapper-support-caqti-2-0-port/17194/3>

Continuing this thread, Chukwuma announced
──────────────────────────────────────────

I recently implemented a database connection using caqti last 2 weeks
and wrote a blog about it. Here it is,
<https://fearful-odds.rocks/blog/postgres-caqti-pooling-ocaml-2025/>

I would like to listen to your feedback or comments regarding my
approach. Cheers

Outreachy Demo Day August 2025
══════════════════════════════

Archive:
<https://discuss.ocaml.org/t/outreachy-demo-day-august-2025/17167/7>

Continuing this thread, Patrick Ferris announced
────────────────────────────────────────────────

For those that could not join us live, the presentations [have now
been uploaded to watch.ocaml.org] – thank you everyone who attended
and congratulations once again to our fantastic Outreachy interns
@pawaskar-shreya and @kemsguy7, and a big thanks to our mentors
@gridbugs and [Michael Dales] :two_hump_camel: !

[have now been uploaded to watch.ocaml.org]
<https://watch.ocaml.org/w/kZJRFM6iw9ug9BLNjEgKeH>

[Michael Dales] <https://digitalflapjack.com/>

Other OCaml News
════════════════

From the ocaml.org blog
───────────────────────

Here are links from many OCaml blogs aggregated at [the ocaml.org
blog].

• [Upcoming OCaml Events]
• [GeoTessera Python library released for geospatial embeddings]
• [Mosaic Terminal User Interface]
• [Building Database Layer in OCaml: From UUID v7 to Standardized
Error Handling]
• [Rust for Everyone!]
• [Using ocaml-lsp-server via an MCP server]
• [Terminal GUI for ocluster monitoring]
• [Modern PostgreSQL Connection Pooling in OCaml (2025): Caqti + Dream
+ Lwt]
• [A ZFS Scaling Adventure]
• [Label Maker in js_of_ocaml using Claude]

[the ocaml.org blog] <https://ocaml.org/blog/>

[Upcoming OCaml Events] <https://ocaml.org/events>

[GeoTessera Python library released for geospatial embeddings]
<https://anil.recoil.org/notes/geotessera-python>

[Mosaic Terminal User Interface]
<https://www.tunbury.org/2025/08/31/mless/>

[Building Database Layer in OCaml: From UUID v7 to Standardized Error
Handling]
<https://fearful-odds.rocks/blog/database-service-layer-sprint>

[Rust for Everyone!]
<https://www.youtube.com/watch/R0dP-QR5wQo?version=3>

[Using ocaml-lsp-server via an MCP server]
<https://jon.recoil.org/blog/2025/08/ocaml-lsp-mcp.html>

[Terminal GUI for ocluster monitoring]
<https://www.tunbury.org/2025/08/24/ocluster-monitor/>

[Modern PostgreSQL Connection Pooling in OCaml (2025): Caqti + Dream +
Lwt] <https://fearful-odds.rocks/blog/postgres-caqti-pooling-ocaml-2025>

[A ZFS Scaling Adventure]
<https://www.tunbury.org/2025/08/23/zfs-scaling/>

[Label Maker in js_of_ocaml using Claude]
<https://www.tunbury.org/2025/08/22/label-maker/>

Old CWN
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If you happen to miss a CWN, you can [send me a message] and I'll mail
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[Alan Schmitt]

[send me a message] <mailto:alan.schmitt@polytechnique.org>

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[Alan Schmitt] <https://alan.petitepomme.net/>

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