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

[Alan Schmitt <alan.schmitt@polytechnique.org>]

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Hello

Here is the latest OCaml Weekly News, for the week of November 04 to 11,
2025.

Table of Contents
─────────────────

Opam-repository, signed! conex is in beta now :)
OCaml Platform Newsletter: September to October 2025
Demonstration of the extension literals and constant rewriting features
Old CWN


Opam-repository, signed! conex is in beta now :)
════════════════════════════════════════════════

  Archive:
  <https://discuss.ocaml.org/t/opam-repository-signed-conex-is-in-beta-now/17461/1>


Hannes Mehnert announced
────────────────────────

  Dear everyone,

  we’re proud to announce that conex, in an initial version, is now
  live! You can receive signed updates of the opam-repository. A quick
  guide:

  To setup opam with conex on your machine, you need to install conex
  (and/or conex-mirage-crypto, see below) - currently only available as
  opam package (sorry about the bootstrap problem - hopefully it will be
  integrated into opam at some time).

  Then, in your “\~/.opam/config” you need to specify the
  [repository-validation-command]:

  ┌────
  │ repository-validation-command: [
  │   "/path/to/conex_verify_mirage_crypto"
  │   "--quorum=%{quorum}%"
  │   "--trust-anchors=%{anchors}%"
  │   "--repository=%{repo}%" {incremental}
  │   "--dir=%{dir}%" {!incremental}
  │   "--patch=%{patch}%" {incremental}
  │   "--incremental" {incremental}
  │ ]
  └────

  Instead of “conex_verify_mirage_crypto”, you can as well use
  “conex_verify_openssl” (fewer dependencies, calls out to OpenSSL as
  the cryptographic provider, is slower).

  Then you can run `opam repo add conex-robur https://conex.robur.coop 1
  sha256=ad5eb0e4a77abfbc6c1bb5661eba46049404e0222588dd059c87f12436d41a28'. Thereafter
  you can `opam repo remove default', and then you’re only using signed
  metadata. The “1” is the quorum of root keys for signatures to be
  valid, the
  “sha256=ad5eb0e4a77abfbc6c1bb5661eba46049404e0222588dd059c87f12436d41a28”
  is the hash of the public root key.

  Read the full article at
  <https://hannes.robur.coop/Posts/ConexRunning> – happy to receive
  feedback.

  The development of conex is supported by the [OCaml Software
  Foundation] and by [ahrefs].


[repository-validation-command]
<https://opam.ocaml.org/doc/Manual.html#configfield-repository-validation-command>

[OCaml Software Foundation] <https://ocaml-sf.org/>

[ahrefs] <https://ahrefs.com/>


OCaml Platform Newsletter: September to October 2025
════════════════════════════════════════════════════

  Archive:
  <https://discuss.ocaml.org/t/ocaml-platform-newsletter-september-to-october-2025/17462/1>


Sabine Schmaltz announced
─────────────────────────

  Welcome to the sixteenth edition of the OCaml Platform newsletter!

  In this September to October 2025 edition, we are excited to bring you
  the latest on the OCaml Platform, continuing our tradition of
  highlighting recent developments as seen in [previous editions]. To
  understand the direction we're headed, especially regarding
  development workflows and user experience improvements, check out our
  [roadmap].

  You can [subscribe to this newsletter on LinkedIn]!

  *Highlights:*

  • *OCaml 5.4.0 Released*: Major stable release featuring labelled
     tuples, immutable arrays, unified array literal syntax, atomic
     record fields, and four new standard library modules
  • *Security Response Team Established*: New team formed to handle
     security vulnerabilities in the OCaml ecosystem
  • *Enhanced Editor Support*: OCaml-LSP 1.24.0 and Merlin 5.6 bring
     improved project navigation and performance optimizations
  • *OCaml.org Reorganization*: Clear separation between news about
     production-ready features and releases (OCaml Changelog) and
     ongoing work and experimental features (Backstage OCaml)
  • *Experimental Tools Progress*: Gospel ecosystem tools ready for
     testing, new ocaml.nvim plugin for Neovim users, and experimental
     Merlin branch using domains and effects

  *OCaml Changelog:*

  • [OCaml.org: Introducing Backstage OCaml - Separate Feeds for Stable
    and Experimental Features] (Oct 8, 2025)
  • [OCaml Security Response Team Established] (Oct 3, 2025)

  *Backstage OCaml:*

  • [Gospel Ecosystem: Tools Ready to Try, Language Evolving] (Oct 15,
    2025)
  • [Backstage OCaml: ocaml.nvim - A Neovim Plugin for OCaml] (Oct 14,
    2025)
  • [Backstage OCaml: You Can Try the Experimental Branch of Merlin That
    Uses Domains and Effects] (Oct 8, 2025)

  *Stable Releases:*

  • [Release of OCaml 5.4.0] (Oct 9, 2025)
  • [opam-publish 2.7.0] (Oct 7, 2025)
  • [OCaml-LSP 1.24.0] (Oct 4, 2025)
  • [Merlin 5.6-503 and 5.6-504] (Oct 4, 2025)
  • [OCaml-LSP 1.23.1] (Oct 3, 2025)
  • [Ppxlib 0.36.2] (Oct 1, 2025)
  • [ocp-indent 1.9.0] (Oct 1, 2025)
  • [opam-publish 2.6.0] (Sep 19, 2025)
  • [Dune 3.20.2] (Sep 10, 2025)

  *Unstable Releases:*

  • [First release candidate for OCaml 5.4.0] (Sep 29, 2025)
  • [Second beta release of OCaml 5.4.0] (Sep 9, 2025)


[previous editions] <https://discuss.ocaml.org/tag/platform-newsletter>

[roadmap] <https://ocaml.org/docs/platform-roadmap>

[subscribe to this newsletter on LinkedIn]
<https://www.linkedin.com/newsletters/ocaml-platform-newsletter-7305270694567661568/>

[OCaml.org: Introducing Backstage OCaml - Separate Feeds for Stable and
Experimental Features]
<https://ocaml.org/changelog/2025-10-08-introducing-backstage-ocaml>

[OCaml Security Response Team Established]
<https://ocaml.org/changelog/2025-10-03-security-team>

[Gospel Ecosystem: Tools Ready to Try, Language Evolving]
<https://ocaml.org/backstage/2025-10-15-gospel-language-evolving>

[Backstage OCaml: ocaml.nvim - A Neovim Plugin for OCaml]
<https://ocaml.org/backstage/2025-10-14-ocaml-nvim-a-neovim-plugin-for-ocaml>

[Backstage OCaml: You Can Try the Experimental Branch of Merlin That
Uses Domains and Effects]
<https://ocaml.org/backstage/2025-10-08-merlin-domains>

[Release of OCaml 5.4.0]
<https://ocaml.org/changelog/2025-10-09-ocaml-540>

[opam-publish 2.7.0]
<https://ocaml.org/changelog/2025-10-07-opam-publish-2-7-0>

[OCaml-LSP 1.24.0]
<https://ocaml.org/changelog/2025-10-04-ocaml-lsp-1240>

[Merlin 5.6-503 and 5.6-504]
<https://ocaml.org/changelog/2025-10-04-merlin-v56-503-and-504>

[OCaml-LSP 1.23.1]
<https://ocaml.org/changelog/2025-10-03-ocaml-lsp-1231>

[Ppxlib 0.36.2] <https://ocaml.org/changelog/2025-10-01-ppxlib-0362>

[ocp-indent 1.9.0]
<https://ocaml.org/changelog/2025-10-01-ocp-indent-190>

[opam-publish 2.6.0]
<https://ocaml.org/changelog/2025-09-19-opam-publish-2-6-0>

[Dune 3.20.2] <https://ocaml.org/changelog/2025-09-10-dune3202>

[First release candidate for OCaml 5.4.0]
<https://ocaml.org/backstage/2025-09-29-ocaml-540-rc1>

[Second beta release of OCaml 5.4.0]
<https://ocaml.org/backstage/2025-09-09-ocaml-540-beta2>

OCaml Compiler
╌╌╌╌╌╌╌╌╌╌╌╌╌╌

◊ OCaml 5.4.0 Stable Release

  The [October 9, 2025 release of OCaml 5.4.0] represents a major
  milestone with significant language enhancements. After two beta
  releases and a release candidate in September, the stable version
  delivers:

  *Language Features:*

  • *Labelled tuples*: Enable better documentation and type safety with
     labels on tuple fields

    ┌────
    │ let ( * ) (x,~dx) (y,~dx:dy) = x*.y, ~dx:(x *. dy +. y *. dx)
    └────

  • *Immutable arrays* (`'a iarray'): Covariant arrays for safer
     concurrent programming
  • *Unified array literal syntax*: `[| ... |]' now works for `'a
     array', `'a iarray', and `floatarray'
  • *Atomic record fields*: New `[@atomic]' attribute with `Atomic.Loc'
     submodule for lock-free concurrent access

  *Standard Library Additions:*

  • `Pair': Utility functions for pairs
  • `Pqueue': Priority queue implementation
  • `Repr': Explicit functions for physical equality and comparison
  • `Iarray': Operations on immutable arrays

  *Runtime Improvements:*

  • Frame pointers support for ARM64 (Linux and macOS)
  • Performance fix for Apple Silicon (using `stlr' instead of `dmb
    ishld; str')
  • Software prefetching for ARM64, s390x, PPC64, and RISC-V
  • Restored "memory cleanup upon exit" mode

  The [September beta releases] and [release candidate] demonstrated the
  maturity of the release, with only minor TSAN and metadata fixes
  needed.


  [October 9, 2025 release of OCaml 5.4.0]
  <https://ocaml.org/changelog/2025-10-09-ocaml-540>

  [September beta releases]
  <https://ocaml.org/backstage/2025-09-09-ocaml-540-beta2>

  [release candidate]
  <https://ocaml.org/backstage/2025-09-29-ocaml-540-rc1>


◊ WIP: Relocatable OCaml

  Work on *Relocatable OCaml* is progressing toward inclusion in OCaml
  5.5, with implementation PRs opened by David Allsopp in September. The
  changes are undergoing review from Samuel Hym, Jonah Beckford, and
  others.

  *What Relocatable OCaml Enables:*

  This feature allows the OCaml compiler and its associated tools to be
  moved to different filesystem locations after installation without
  breaking functionality. Key benefits include:

  • Binary distributions that work regardless of installation path
  • Improved flexibility for package managers organizing OCaml
    installations
  • Bundling of specific OCaml versions by developer tools without path
    conflicts
  • Simplified cross-platform distribution

  *Current Status:*

  The implementation is in active review with ongoing responses to
  feedback. The core development team is likely to review the changes at
  an upcoming meeting, targeting inclusion in OCaml 5.5.

  For technical details about the implementation approach and its
  implications for the ecosystem, see David Allsopp's [blog post on
  Relocatable OCaml] and the associated [Discuss thread].


  [blog post on Relocatable OCaml]
  <https://www.dra27.uk/blog/platform/2025/09/15/relocatable-ocaml.html>

  [Discuss thread] <https://discuss.ocaml.org/t/relocatable-ocaml/17253>


Build System
╌╌╌╌╌╌╌╌╌╌╌╌

◊ Dune

  [Dune 3.20.2] (September 10, 2025) provides bug fixes and stability
  improvements for the 3.20 series.


  [Dune 3.20.2] <https://ocaml.org/changelog/2025-09-10-dune3202>

  ◊ Experimental: Dune Package Management

    We keep exploring:

    • *Portable External Dependencies*: An approach for storing system
       package dependencies in a platform-agnostic format, allowing
       projects to maintain a single specification that resolves
       correctly across Linux, macOS, and Windows environments, ensuring
       consistent builds regardless of platform-specific package naming
       and versioning differences.
    • *Portable Lock Directories*: Lock directories that work
       consistently across different operating systems and
       architectures, addressing the current limitation where
       platform-specific dependency resolutions prevent teams from
       sharing lock files through version control in heterogeneous
       development environments.
    • *Lock Directories as Build Targets*: Currently, the solver that
       comes up with a set of compatible dependencies needs to be run by
       the user explicitely (using `dune pkg lock'), but in the future
       we intend to create build plans implicitly via Dune build
       rules. This should make make package management simpler to use as
       it requires fewer user actions and does not require putting
       verbose lock directories into the project source
       directories. This change also paves the way for automatic
       relocking when dependencies change, including in watch mode.

    These features remain under active development and should not be
    relied on in production. However, we encourage cautious adoption of
    Dune Package Management itself for users comfortable with
    bleeding-edge tools that may still change. Dune package management
    is available in the stable release of Dune, as an experimental
    feature.

    *Dune Maintained by*: Rudi Grinberg (@rgrinberg, Jane Street),
     Nicolás Ojeda Bär (@nojb, LexiFi), Marek Kubica
     (@Leonidas-from-XIV, Tarides), Ali Caglayan (@Alizter, Tarides),
     Etienne Millon (@emillon), Stephen Sherratt (@gridbugs, Tarides),
     Antonio Nuno Monteiro (@anmonteiro), Etienne Marais (@maiste)


Package Management
╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌

◊ opam-publish

  We celebrate two releases of opam-publish: [*opam-publish 2.6.0*]
  (September 19, 2025) and [*opam-publish 2.7.0*] (October 7, 2025).

  These releases make it easier to automate package publishing,
  particularly benefiting projects with continuous deployment pipelines.

  *Maintained by*: Raja Boujbel (@rjbou, OCamlPro), Kate Deplaix
   (@kit-ty-kate, Ahrefs)


  [*opam-publish 2.6.0*]
  <https://ocaml.org/changelog/2025-09-19-opam-publish-2-6-0>

  [*opam-publish 2.7.0*]
  <https://ocaml.org/changelog/2025-10-07-opam-publish-2-7-0>


Editor Tools
╌╌╌╌╌╌╌╌╌╌╌╌

  *Roadmap: [Edit / (W19) Navigate Code]*


[Edit / (W19) Navigate Code]
<https://ocaml.org/tools/platform-roadmap#w19-navigate-code>

◊ OCaml-LSP Server and Merlin

  September and October saw significant updates to editor support:


  ◊ Stable Releases

    • [*OCaml-LSP 1.24.0*] (October 4, 2025): Major release with
      improved project navigation and performance optimizations
    • [*OCaml-LSP 1.23.1*] (October 3, 2025): Bug fix release
    • [*Merlin 5.6-503 and 5.6-504*] (October 4, 2025): Support for
      OCaml 5.3 and 5.4 with performance improvements


    [*OCaml-LSP 1.24.0*]
    <https://ocaml.org/changelog/2025-10-04-ocaml-lsp-1240>

    [*OCaml-LSP 1.23.1*]
    <https://ocaml.org/changelog/2025-10-03-ocaml-lsp-1231>

    [*Merlin 5.6-503 and 5.6-504*]
    <https://ocaml.org/changelog/2025-10-04-merlin-v56-503-and-504>


  ◊ Experimental: Merlin with Domains and Effects

    The [experimental Merlin branch using domains and effects] offers
    potential performance improvements through parallelization. This
    experimental version is available for testing but not recommended
    for production use.


    [experimental Merlin branch using domains and effects]
    <https://ocaml.org/backstage/2025-10-08-merlin-domains>


◊ ocp-indent

  [*ocp-indent 1.9.0*] (October 1, 2025): Updates for OCaml 5.4.0
  compatibility and improved formatting rules.


  [*ocp-indent 1.9.0*]
  <https://ocaml.org/changelog/2025-10-01-ocp-indent-190>


◊ Experimental: ocaml.nvim

  [Tarides announced ocaml.nvim], a new Neovim plugin for OCaml
  development. This experimental plugin serves as the Neovim counterpart
  to ocaml-eglot, leveraging LSP for modern editor features.

  *OCaml LSP Server maintained by*: Ulysse Gérard (@voodoos, Tarides),
   Xavier Van de Woestyne (@xvw, Tarides), Rudi Grinberg (@rgrinberg,
   Jane Street)

  *Merlin maintained by*: Ulysse Gérard (@voodoos, Tarides), Xavier Van
   de Woestyne (@xvw, Tarides), Muluh Godson (@PizieDust, Tarides),


  [Tarides announced ocaml.nvim]
  <https://ocaml.org/backstage/2025-10-14-ocaml-nvim-a-neovim-plugin-for-ocaml>


Documentation and PPX Tools
╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌

◊ Ppxlib

  [*Ppxlib 0.36.2*] (October 1, 2025): Compatibility updates for OCaml
  5.4.0 and fixes for AST handling.

  *Maintained by*: Nathan Rebours (@NathanReb)


  [*Ppxlib 0.36.2*] <https://ocaml.org/changelog/2025-10-01-ppxlib-0362>


Gospel Ecosystem (Experimental)
╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌

  The Gospel formal specification ecosystem now offers tools for
  experimental specification-driven testing, as detailed in ["Gospel
  Ecosystem: Tools Ready to Try, Language Evolving"].

  *Available Tools:*

  • *Ortac/QCheck-STM* generates property-based tests from Gospel
     specifications written in `.mli' files. The tool won the TACAS 2025
     Best Tool Paper award and can automatically produce comprehensive
     test suites from formal specifications. While the underlying Gospel
     language syntax may still change, the testing workflow is stable
     enough for experimental use in development environments.

  *Current Status:*

  The tools work well for isolated modules where you can write
  specifications and generate tests, but the Gospel language itself
  remains under active development with potential breaking changes
  ahead. Teams using these tools should be prepared to update
  specifications as the language evolves. This makes the ecosystem
  suitable for greenfield projects, experimental codebases, or
  well-isolated components where specification changes won't cascade
  through large systems.


["Gospel Ecosystem: Tools Ready to Try, Language Evolving"]
<https://ocaml.org/backstage/2025-10-15-gospel-language-evolving>


Platform Infrastructure
╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌

◊ OCaml Security Response Team

  The [establishment of the OCaml Security Response Team] (October 3,
  2025) marks an important step in ecosystem maturity. The team will
  handle security vulnerabilities following established disclosure
  practices.


  [establishment of the OCaml Security Response Team]
  <https://ocaml.org/changelog/2025-10-03-security-team>


◊ OCaml.org Reorganization

  The [newly introduced separation of OCaml Changelog and Backstage
  OCaml] provides clearer communication:

  • *OCaml Changelog*: Official stable releases and production-ready
     updates
  • *Backstage OCaml*: Experimental releases, work-in-progress, and
     development opportunities

  This helps readers distinguish more easily between what's ready for
  production use and what's still experimental.


  [newly introduced separation of OCaml Changelog and Backstage OCaml]
  <https://ocaml.org/changelog/2025-10-08-introducing-backstage-ocaml>


Community Events
╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌

◊ FUN OCaml 2025

  The FUN OCaml conference took place on *September 15-16, 2025* in
  Warsaw, Poland, featuring talks on practical OCaml development,
  industry applications, and community projects. The [FUN OCaml 2025
  program and speaker lineup] showcases the diverse ecosystem of OCaml
  in production. Video recordings of all presentations will be available
  soon for those who couldn't attend in person.


  [FUN OCaml 2025 program and speaker lineup]
  <https://fun-ocaml.com/2025/>


◊ OCaml Workshop 2025

  The OCaml Users and Developers Workshop was held on *October 17, 2025*
  in Singapore, co-located with ICFP/SPLASH, bringing together
  researchers and practitioners. You can find the list of presentations
  and a link to the video recordings on [the OCaml Workshop 2025 page on
  OCaml.org]!

  —

  We're pleased to see the successful release of OCaml 5.4.0, marking a
  significant milestone with labelled tuples, immutable arrays, and
  atomic fields. The establishment of the Security Response Team and the
  reorganization of OCaml.org demonstrate the ecosystem's growing
  maturity.

  The clear separation between stable releases and experimental work
  helps the community make informed decisions about tool adoption. While
  experimental features in the Dune Developer Preview, ocaml.nvim, and
  Gospel ecosystem show promising directions, they remain in testing and
  should not be used in production.

  As always, we encourage feedback and contributions from the community
  as we continue to improve the OCaml Platform ecosystem.


  [the OCaml Workshop 2025 page on OCaml.org]
  <https://ocaml.org/conferences/ocaml-workshop-2025>


Demonstration of the extension literals and constant rewriting features
═══════════════════════════════════════════════════════════════════════

  Archive:
  <https://discuss.ocaml.org/t/demonstration-of-the-extension-literals-and-constant-rewriting-features/17466/1>


Mikhail announced
─────────────────

  Yo! :yoyo: :waving_hand:

  I started learning the beautiful [ppxlib] library and found
  interesting information in their documentation about OCaml's syntax
  features, such as extension literals - the ability to append a
  one-letter identifier to numeric literals. I was surprised at how easy
  it was to do this.

  Because I was inspired by this, I wrote a demonstration project
  (located in my [GitHub repository]) to show how to use it to implement
  metric system support in code.

  ┌────
  │ utop # 5m;; 
  │ - : Metric.Meter.t = 5
  │ 
  │ utop # Metric.Meter.(1m + 10m);;
  │ - : Metric.Meter.t = 11
  └────

  References:
  • OCaml – Language extensions – [Extension literals]
  • Ppxlib – Context-free transformation – [Constant Rewriting]()


[ppxlib] <https://github.com/ocaml-ppx/ppxlib>

[GitHub repository] <https://github.com/dx3mod/metric_syntax>

[Extension literals]
<https://ocaml.org/manual/5.4/extensionsyntax.html#ss:extension-literals>


Old CWN
═══════

  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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