OCaml Weekly News

I’d like to announce release of version 2.0.0 of routes to the ocaml package registry.

Routes provides a DSL for typed bi-directional URI dispatch. It allows writing route definitions that can be used for both matching, and printing URI paths. The internal representation of the router uses a trie to perform route matching.

I’m happy to announce the release of Domainslib 0.5.0.

Domainslib is a parallel programming library for the upcoming OCaml 5. Domainslib provides support for parallel operations such as parallel_for, async~/~await tasks etc. with an efficient work-stealing mechanism in its core. Tasks are expressed with effect handlers, enabling efficient nested parallelism.

You can give it a spin with the 5.0.0~alpha1 compiler. For examples of Domainslib programs, here is a tutorial on parallel programming with domainslib, KC’s hands on tutorial at the Tarides retreat, and another one Marek and I did at ICFP 2022.

Submissions of interesting Domainslib benchmarks appreciated at sandmark. Results of existing ones can be viewed at https://sandmark.tarides.com/ under the parallel benchamrks tab. Please feel free to add your multicore/effects libraries and experiments to awesome-multicore-ocaml.

Changes from the previous release:

• Bug fix for parallel_for_reduce on empty loops.
• Make Chan.t and Task.promise injective Make Chan.t and Task.promise injective ocaml-multicore/domainslib#69
• Add lockfree dependency remove Ws_deque module ocaml-multicore/domainslib#70
• CI fixes (Add alpha repo to GitHub Actions ocaml-multicore/domainslib#73, Run 5.0.0~alpha0 in the CI ocaml-multicore/domainslib#76)
• Breaking change: Rename num_additional_domains to num_domains for setup_pool
• Documentation updates (Use invalid_arg ocaml-multicore/domainslib#80, Document that non-commutative operators are okay ocaml-multicore/domainslib#81, Explain what will happen with an empty pool ocaml-multicore/domainslib#82)

Dear community, the videos of the talks given at the ML workshop in September 2022 in Ljubljana are now available. Enjoy!

The release of OCaml 5.0.0 is drawing near.

After two alpha releases, we have released a first beta version to help you update your softwares and libraries ahead of the release (see below for the installation instructions). The standard library has been stabilized and many opam packages already work with this release. If you find any bugs, please report them here:

https://github.com/ocaml/ocaml/issues

Compared to the last alpha release, this beta contains many small internal runtime fixes (in particular in the systhreads library). At the user level, the interfaces of the Domain and Effect modules have been tweaked to be more forward-compatible:

• Exceptions related to effects are now defined in the Effect module.
• The value Domain.recommended_domain_count is no longer a constant and the function Domain.at_each_spawn has been removed.

With those changes, the standard library should be stable now. The final release of OCaml 5.0.0 is currently expected to be in December.

If you are interested by the ongoing list of bug fixes, the updated change log for OCaml 5.0.0 is available at:

https://github.com/ocaml/ocaml/blob/5.0/Changes

You can also follow the state of the opam ecosystem on

https://github.com/ocaml/opam-repository/issues/21526

and

http://check.ocamllabs.io/

A short summary of the changes since the last alpha release is also available below.

A new 0.2.0 version has just been released. Thanks to all the contributors (including Outreachy applicants!), there’s a lot of nice additions including:

• to_yaml and of_yaml attributes allowing you to add custom encoders and decoders
• a skip_unknown flag for ignoring yaml keys so you can partially decode yaml values
• a default attribute
• [@@deriving yaml] is now an alias to [@@deriving to_yaml] and [@@ deriving of_yaml] so you can get decoders, encoders or both.

See the documentation in the README: https://github.com/patricoferris/ppx_deriving_yaml

For people interested in good documentation for their projects, but need a bit more from odoc.

I wanted to make a place where the broader OCaml community can experiment and propose odoc features: https://diskuv.github.io/odoc-sandbox/

I had two goals for the sandbox:

• Let you visually see any proposals for new features to odoc. Hopefully this will make scoping the proposal easier.
• No one should be blocked. Assuming the proposal is ok, it may take months (or even years) to implement. Any early adopter could use the custom Dune rules from the experiment to adopt in their own projects. Early adoption would be complex (custom Dune rules) but since the syntax shouldn’t change they won’t have to throw out their documentation.

I have one proposal in the sandbox and more will come later; there are also a few experiments using Sphinx and Markdown tools.

The first proposal would translate an odoc verbatim block:

{v
::code-block:: LANGUAGE

source code
v}

into syntax highlighted code. The visual results and the original .mli are available in experiment 400.

As I mentioned earlier, it has Dune rules which can be copied if you need it in your own projects. I don’t precisely know how it would be implemented for real in odoc (probably it would be a .mli transformer) but that is not the point. Instead if you have an implementation idea or simply love/hate the proposal, you can just go to GitHub and file an issue at https://github.com/diskuv/odoc-sandbox/issues.

In anticipation of the forthcoming OCaml 5 release—and hot on the heels of its beta release—we are thrilled to announce the alpha release of the OCaml Platform Installer.

As a reminder, the OCaml Platform is the recommended toolchain for developers to work with OCaml.

The Platform Installer allows the user to easily setup OCaml’s development environment, both for a first-time installation and for any new opam switches.

You can try it now by following the [installation instructions](#platform-installer-2), but TL;DR, you can install it with

$ bash < <(curl -sL https://github.com/tarides/ocaml-platform-installer/releases/latest/download/installer.sh)

And run it to install the Platform in your opam switch with

$ ocaml-platform

Don’t hesitate to open an issue if you encounter any problem!

I am pleased to announce dkml-dune-dsl, an embedding of Dune inside OCaml (aka. an eDSL) for developers that need to simplify complex Dune logic. An excerpt from the README:

Once installed you will be able to write DSL expressions like:

open DkmlDuneDsl

module Build (I : Dune.SYM) = struct
  open I

  let res =
    [
      rule
        [
          target "{{{ name }}}.txt";
          action
            (with_stdout_to "%{target}"
              (echo [ "{{{ age }}}" ]));
        ];
    ]
end

that are run over the parameters in a JSON file:

{
  "param-sets": [
    {"name": "batman", "age": 39},
    {"name": "robin", "age": 24}
  ]
}

You can do also do aggregation or, if you are really adventurous, define your own interpreter. Even if you don’t use parameterization you get things you take for granted with OCaml: type-safety, auto-complete and `let` constants.

The full documentation including installation instructions and examples are available in the README.

A few cautionary notes:

• The current version (0.1.0 as of Oct 17 2022) does not have 100% coverage of all Dune expressions; it just has the parts of Dune I’ve needed in my own projects. That includes an encoding of the Ordered Set Language and virtual libraries but not (for example) select forms, plugins, ctypes and lex/yacc. But I strongly suspect the same people who need a tool like dkml-dune-dsl are the same people who can easily contribute a PR to add any parts of Dune they need.
• The API is unstable; if someone adds more Dune expressions they may have to tweak the API. And I haven’t settled on whether the API needs some first-class features to track Dune’s (lang dune X.Y.Z) versioning.
• This is not blessed in any way by the Dune team! Hopefully they don’t mind though.

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

• Real World OCaml Book Giveaway!
• 8 OCaml Libraries to Make Your Life Easier
• ICFP 2022 Review