[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 March 17 to 24,
2026.

Table of Contents
─────────────────

Introducing atdml (experimental)
Experimental module imports in ATD (ATD 4.0.0)
Dune 3.22
Parseff: parser combinator library for OCaml 5
Outreachy Demo Day for December 2025 Round
Old CWN


Introducing atdml (experimental)
════════════════════════════════

  Archive:
  <https://discuss.ocaml.org/t/ann-introducing-atdml-experimental/17908/1>


Martin Jambon announced
───────────────────────

  ATD 4.0.0 was released today on opam.

  This release introduces *atdml*, an experimental replacement for
  atdgen.

  The goal is to modernize the implementation and make it easier to
  extend, while keeping compatibility with existing ATD workflows.

  Here's a sample input file `example.atd':
  ┌────
  │ type location = {
  │   row: int;
  │   column: int;
  │   ?file: string option;
  │ }
  └────

  Atdml is invoked as follows, normally by the build system:
  ┌────
  │ $ atdml example.atd
  └────

  It produces a pair of mli and ml files. This is `example.mli':
  ┌────
  │ (* Auto-generated from "example.atd" by atdml. *)
  │ 
  │ type location = {
  │   row: int;
  │   column: int;
  │   file: string option;
  │ }
  │ 
  │ val create_location : row:int -> column:int -> ?file:string -> unit -> location
  │ val location_of_yojson : Yojson.Safe.t -> location
  │ val yojson_of_location : location -> Yojson.Safe.t
  │ val location_of_json : string -> location
  │ val json_of_location : location -> string
  │ 
  │ module Location : sig
  │   type nonrec t = location
  │   val create : row:int -> column:int -> ?file:string -> unit -> t
  │   val of_yojson : Yojson.Safe.t -> t
  │   val to_yojson : t -> Yojson.Safe.t
  │   val of_json : string -> t
  │   val to_json : t -> string
  │ end
  └────

  Release notes: <https://github.com/ahrefs/atd/releases/tag/4.0.0>

  Documentation: <https://atd.readthedocs.io/>

  Project page: <https://github.com/ahrefs/atd>


Experimental module imports in ATD (ATD 4.0.0)
══════════════════════════════════════════════

  Archive:
  <https://discuss.ocaml.org/t/ann-experimental-module-imports-in-atd-atd-4-0-0/17909/1>


Martin Jambon announced
───────────────────────

  ATD 4.0.0 adds experimental support for imports between ATD files.

  This allows splitting schemas across multiple files in a natural way.

  Currently supported in:
  • atdml (OCaml)
  • atdpy (Python)
  • atdts (TypeScript)

  Example:
  ┌────
  │ from utils as u import email
  │ 
  │ type email_addresses = u.email list
  └────

  Details: <https://github.com/ahrefs/atd/releases/tag/4.0.0>

  For an earlier discussion of the design, see
  <https://discuss.ocaml.org/t/rfc-multifile-atd-definition-support-via-import-statements/17881>].


Dune 3.22
═════════

  Archive: <https://discuss.ocaml.org/t/ann-dune-3-22/17912/1>


Shon announced
──────────────

  The Dune team is pleased to announce [the release of dune 3.22.0].

  In addition to many fixes and small improvements, notable highlights
  of this release include:

  • Fixes to the dune cache on Windows, thanks to [@Nevor] in
    [ocaml/dune#13713].
  • New tracing functionality, to inspect and diagnose the build
    processes thanks to [@rgrinberg] across many PRs. See [the
    documentation].
  • Addition of the `dune-action-trace' library, to instrument trace
    emission, thanks to [@rgrinberg].
  • Support for generating odoc documentation in markdown via the
    `@doc-markdown' build alias thanks to [@davesnx] [ocaml/dune#12581].
  • Full support for OxCaml's parameterised libraries, thanks to
    [@art-w] and [@maiste]. To learn more, see [the docs].

  See [the full changelog] for all new features and fixes, and for
  attribution to the contributors who made it all possible. Thank you,
  contributors!

  If you encounter a problem with this release, please report it in [our
  issue tracker].


[the release of dune 3.22.0]
<https://github.com/ocaml/dune/releases/tag/3.22.0>

[@Nevor] <https://github.com/Nevor>

[ocaml/dune#13713] <https://github.com/ocaml/dune/pull/13713>

[@rgrinberg] <https://github.com/rgrinberg>

[the documentation]
<https://dune.readthedocs.io/en/stable/hacking.html#inspecting-traces-with-jq>

[@davesnx] <https://github.com/davesnx>

[ocaml/dune#12581] <https://github.com/ocaml/dune/pull/12581>

[@art-w] <https://github.com/art-w>

[@maiste] <https://github.com/maiste>

[the docs]
<https://dune.readthedocs.io/en/stable/tutorials/oxcaml-parameterized-library/index.html>

[the full changelog] <https://github.com/ocaml/dune/releases/tag/3.22.0>

[our issue tracker] <https://github.com/ocaml/dune/issues>


Parseff: parser combinator library for OCaml 5
══════════════════════════════════════════════

  Archive:
  <https://discuss.ocaml.org/t/ann-parseff-parser-combinator-library-for-ocaml-5/17914/1>


David Sancho announced
──────────────────────

  Hi everyone,

  I’m sharing *Parseff*, a parser combinator library for *OCaml 5*.

  If you like parser combinators but don’t love writing everything in
  monadic style, Parseff is built for that. Parsers are plain functions
  (`unit -> 'a') and you compose them in direct style, while Parseff
  handles backtracking and streaming under the hood (using effects!)


Why Parseff
╌╌╌╌╌╌╌╌╌╌╌

  • *Direct-style API*: write sequential OCaml code, no `>>=', `let*',
     or applicative operator chains required.
  • *Typed errors*: raise domain errors with polymorphic variants via
     `Parseff.error'.
  • *Streaming input*: same parser works with `Parseff.parse' (string)
     and `Parseff.parse_source' (stream).
  • *Zero-copy + fused ops*: span APIs and fused operations for hot
     parsing paths.
  • *Domain-safe execution*: parse calls are self-contained (no global
     mutable state).
  • Automatic backtracking with [`Parseff.or_']
  • Minimal dependency footprint: only `re' for regex


[`Parseff.or_'] <https://davesnx.github.io/parseff/api/combinators/#or_>


Performance
╌╌╌╌╌╌╌╌╌╌╌

  In the included benchmarks, Parseff is faster than Angstrom and
  MParser:

  • around *~2x* in fair comparisons
  • up to *~4x+* with zero-copy optimized paths
  Benchmark details and code are in the repo docs.

  ## Documentation

  I’ve put a lot of effort into the docs (quick start, guides, and API
  pages) to keep Parseff easy to learn. A bit proud of using odoc’s
  Markdown backend plus mdx, I can generate and check examples on the
  fly, so snippets stay type-safe.

  <https://davesnx.github.io/parseff>


Install
╌╌╌╌╌╌╌

  ┌────
  │ opam install parseff -y
  └────


Links
╌╌╌╌╌

  • Docs: <https://davesnx.github.io/parseff/>
  • Comparison guide:
    <https://davesnx.github.io/parseff/guides/comparison/>
  • GitHub: <https://github.com/davesnx/parseff>

  If you try it, I’d really value feedback on: API ergonomics, error
  handling experience or missing combinators or docs gaps!

  Thanks!


Outreachy Demo Day for December 2025 Round
══════════════════════════════════════════

  Archive:
  <https://discuss.ocaml.org/t/outreachy-demo-day-for-december-2025-round/17883/5>


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

  The recording of our (nearly two hour!) meeting is now online:
  <https://watch.ocaml.org/w/8aUqMhFvhQGq4WJLH3ukjA> !

  Thank you to everyone who joined :two_hump_camel:


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]


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


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