OCaml Weekly News

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Here is the latest OCaml Weekly News, for the week of April 18 to 25, 2023.

Table of Contents

Dream development stream + OCaml office hours

Anton Bachin announced

Chat with me while I develop Dream, but also ask any questions at all about OCaml!


I’ll be streaming Dream development on Twitch at 14:00 CEST (Paris time) on most weekdays, and definitely on every Thursday. Each time, I’ll stream for at least one hour.

Tomorrow, on Wednesday, April 19th, at 14:00 CEST, I will be continuing to review the Dream Eio PR by @talex5 and @Willenbrink, adding more detail to and revising the Dream 1.0 roadmap, and generally just be available to talk about anything related to OCaml. We can build toy projects, demos, work out concepts, etc. If you’d like to contribute to Dream, we can discuss good first issues, review your PRs, and collabarote otherwise!

Outside the stream, I can be reached in #webdev on the OCaml Discord or #dream on the Reason Discord. My nickname on both is antron.

In the future, I’d be happy to consider something more interactive than a Twitch stream – something where people can talk back, probably some sort of developer or contributor meeting. But it seems that Twitch is the right place to get started.

Anton Bachin later said

Thanks to everyone for coming to the stream today! We had a pretty good viewership! The next stream is tomorrow, Thursday, April 20th, at the same time: 14:00 CEST.

Today, we got the Eio PR building, and found some problems with it – fixing those problems offline and during the next stream will be a good way to start reviewing the internal changes in detail! We also talked about plans for Dream and discussed some of Dream’s dependencies and developer tools.

I post the next stream time and its topic in the banner image of the stream, so you can easily find out when it’s planned even when the stream is offline. Planned streams are also in the schedule. For weekdays besides Thursday, I’ll decide about streaming a few days in advance.

Suggestions for how to make the stream nicer are welcome :) I try to maintain a good look for my windows and use some goofy VSCode extensions. If we start doing long, boring builds, we can maybe add games for viewers to play or even a cat cam, though I think that is a stretch at this point :) So far, I’ve been able to do all the very slow stuff offline.

As the stream becomes more of a regular occurrence, I’ll stop posting about it here, but I’ll probably continue to announce it in the Reason and OCaml Discords, once I figure out what channels are appropriate for that. Probably #dream and #webdev, respectively.

New release of Menhir (20230415)

François Pottier announced

It is my pleasure to announce a new release of Menhir, with a number of minor improvements.

The change log appears below. The main point of notice is that (when using the code back-end) the default optimization level has been changed from -O 2 to -O 1. So, if you need to keep identical generated code and performance, you should now explicitly pass -O 2 to Menhir.

  opam update
  opam install menhir.20230415


  • When using the code back-end, the default optimization level is now -O 1 instead of -O 2. Some users reported that -O 2 is too aggressive and can cause a blow-up in the size of the code.
  • Tweak the code for compatibility with OCaml 5.1. (Contributed by Florian Angeletti.)
  • The new function MenhirLib.LexerUtil.tabulate makes it easy to run the lexer and parser in two separate phases. This can be useful when one wishes to benchmark them separately.
  • To use the interpreter and print a concrete syntax tree, it used to be necessary to pass both --interpret and --interpret-show-cst. It is now sufficient to pass just --interpret-show-cst. (If both are passed, then only the last one is obeyed.) This fixes the assertion failure that would be observed when --interpret-show-cst alone was used. (Reported by Reed Mullanix.)

Functional web applications running in the browser

Helmut announced

I am pleased to announce the first release of the library fmlib_browser.

If you want to write functional web applications running in the browser the library fmlib_browser might interest you. It allows web applications in the elm style using the much more powerful language ocaml.

I have discovered the elm language some years ago and I am convinced that this kind to write web applications is one important future way to develop web applications. So I wanted to have the same in the ocaml language. Therefore I have developed this library (and of course using js_of_ocaml as the compiler to javascript) and I am quite happy that it works well.

Some simple examples of web applications and the corresponding source code written by using the library fmlib_browser.

Install the library via opam by issuing the command

    opam install fmlib_browser

Benjamin Thomas asked and Helmut replied

Hello @hbr, thanks for sharing your project :)

Did you know about ocaml-vdom before creating this lib?


If yes, why did you create it? How does it differ?

@benjamin-thomas: I know the project ocaml-vdom and the basic idea with respect to virtual dome is very similar. However I wanted to have something more generic.

If you look into the interface of ocaml-vdom you see that e.g. the event handlers are limited to the definitions in the library. With Fmlib_browser you can customize your event handlers completely. My event handlers use elm’s generic concept of decoders to suck any information you want from the events.

The properties in my library are generic. You can create arbitrary javascript value including objects and arrays. In ocaml-vdom you are limited to primitive values like int, float, string and bool.

Furthermore I wanted to have a pretty generic interface between the javascript world and the ocaml world.

The concept of Fmlib_browser is extendible. In the future I want to add features e.g. to start web workers, integrate custom elements to have access e.g. to code mirror.

Timmy 1.0.0, a high level time and calendar library

mefyl announced

I’m pleased to announce the availability on OPAM of the first stable version of Timmy, the library that powers all the time and calendar operations we perform at Routine.

It provides amongst other things:

  • Higher level types for time and calendar values.
  • Uncompromising timezone safety.
  • Timezone with DST support.
  • ISO weeks support.
  • Quality of life operators and common computations on most objects.
  • JavaScript back and forth conversions.

The philosophy and rationale for the library is explained at length in its root module documentation . Comments and contributions very welcome.

Wed, Apr 19 @ 7pm U.S. Central: Jonah Beckford on “What distributing OCaml on Windows gave me (and you)”

Continuing this thread, jbeckford said

Thanks. Reminds me to share the slides: https://diskuv.gitlab.io/books/DkPresentations/Presentations/2023-04-19-hfpug/

I think the recording will be available in several days.

Claude Jager-Rubinson later added

The OCaml Changelog

Thibaut Mattio announced

The OCaml.org team is happy to announce the OCaml Changelog: a feed of the latest releases and feature highlights of the OCaml Compiler, OCaml Platform tools, and other core projects.

Beyond being the easiest way to stay up to date with the activity of official projects, the Changelog serves as a way to discover important new features that might otherwise go unnoticed. For instance, did you know that Dune 3.7 introduced native polling mode for Windows, effectively making watch mode available on Windows (contributed by @nojb and @yams-yams)? Or that we recently released Mdx 2.3.0 with support for running code blocks in mld files (contributed by @jonludlam)? Or that we added new options in OCamlFormat for more consistent vertical formatting of if-else and match statements (contributed by @gpetiot)?

To that end, we’re highlighting important features from the releases with visual demos and explanations of how to use them.

I’ll note that the Changelog is still experimental at this point. We’ve talked with some maintainers of the projects featured on the Changelog, but we’ll need to agree with everyone on what the release process of the tools will look like if we commit to maintaining the Changelog in the long term. Until we’ve reached a consensus, the OCaml.org team will be monitoring the activity of the projects and create the changelog entries, eventually reaching out to maintainers to write announcements and feature highlights.

In the meanwhile, let us know what you think and how we can improve the Changelog, we’re excited to get your feedback!

Happy reading!

OUPS meetup may 2023

zapashcanon announced

The next OUPS meetup will take place on Thursday, 11th of May 2023. It will start at 7pm at the 4 place Jussieu in Paris.

:warning: :trumpet: It will be in the in the Herpin amphitheater in the Esclangon building. :trumpet: :warning:

Please, register on meetup as soon as possible to let us know how many pizza we should order.

For more details, you may check the OUPS’ website .

This month will feature the following talks :

Retrofitting OCaml Modules – Clément Blaudeau

ML modules offer large-scale notions of composition and modularity. Provided as an additional layer on top of the core language, they have proven both vital to the working OCaml and SML programmers, and inspiring to other use-cases and languages. Unfortunately, their meta-theory remains difficult to comprehend, and more recent extensions (abstract signatures, module aliases) lack a complete formalization. Building on a previous translation from ML modules to Fω, we propose a new comprehensive description of a significant subset of OCaml modules, including both applicative and generative functors and transparent ascription – a useful new feature. By exploring the translations both to and from Fω, we provide a complete description of the signature avoidance issue, as well as insights on the limitations and benefits of the path-based approach of OCaml type-sharing.

Formal reasoning rules for the OCaml FFI -- Armaël Guéneau (@Armael)

OCaml provides an FFI mechanism (Foreign Function Interface) allowing OCaml programs to call external functions implemented in C, typically by writing “glue code” helping bridge the two languages. This “glue code” needs to be carefully written and obey a number of rules when interacting with the OCaml runtime (cf chapter 22 of the manual). Failure to follow one of these rules typically result in silent corruption of the program memory, resulting in fatal and hard to debug crashes. This presentation will present ongoing research on formalizing the rules one need to follow to correctly use the OCaml FFI. We will see how a small number of permissions can capture the requirements one must obey in order to write bug-free glue code.

3-year engineering position in Deducteam, Inria Paris-Saclay, France

Frédéric Blanqui announced

Deducteam is offering a 3-year engineering position to help develop, test and maintain tools for proof system interoperability (continuous integration, proof libraries management, searching tools, VSCode interface, etc.). Net taxable monthly salary between 2148 and 4412 euros depending on experience, including social security and 9 weeks holidays/year.

Interested people should send me their CV before 30 July 2023. Applications will be examined over time.

Best regards, Frédéric Blanqui, chair of EuroProofNet. https://blanqui.gitlabpages.inria.fr/

RFC for a distributed process/actor model library

Darren announced

I recently wrote down what’s been brewing in my mind for a bit: a Erlang style process/actor model library in the new OCaml 5 landscape. It is beginning to resemble something I’d use, but I’m curious about what others think.

The repo of the prototype is available at here

The library is built on top of Eio and should place nicely with Eio primitives. Snippet of a runnable example is shown below (debug/main.ml in the repo).


  • Gateway plays roughly the role of Erlang’s BEAM VM.
    • Intention is user can establish TLS tunnels to other gateways to allow distribution.
  • Mailbox.Local API allows skipping the serialization cost when sending things internally
    • Mailbox.Global.t (when implemented) conversely demands serialization procedures during construction.
  • Process a uses selective receive interface (Selective.recv and Selective.Recv.*) to handle timeout and guards/message filtering.
    • A save queue is used underneath per mailbox for messages rejected (for now), following Erlang’s design.
    • Doesn’t seem possible to have a global save queue without also serialising everything.
  • Process b sends a bunch of things a does not care about, wait, then finally sends something a is looking for.
  • Process controller is just largely there to demonstrate one can redirect processes.

Code snippet

(debug/main.ml on repo)

let () =
  let pid_mailbox : Proc.Pid.t Mailbox.Local.t =
    Mailbox.Local.make ()
  let Mailbox.Local.{ send = send_pid; recv = recv_pid } = Mailbox.Local.interface
pid_mailbox in
  let x_mailbox  : x Mailbox.Local.t =
    Mailbox.Local.make ()
  let Mailbox.Local.{ send = send_x; recv = recv_x } = Mailbox.Local.interface
x_mailbox in
  let a =
    Gateway.spawn (fun h ->
        Fmt.epr "a: my pid is %a@." Proc.Pid.pp (Proc.Handle.pid h);

        let _, send_to = recv_pid h in
        Fmt.epr "a: received instruction to send to %a@." Proc.Pid.pp send_to;
        send_x h (send_to, A);
        send_x h (send_to, A);
        send_x h (send_to, A);

        let rec aux () =
          let success =
            Selective.recv h
              ~timeout:(1.0, fun () ->
                  Fmt.epr "a: I haven't received anything useful yet@.";
                case_local x_mailbox
                    entry ~guard:(fun (from, x) -> x = A)
                      (fun (from, msg) ->
                         Fmt.epr "a: received %a from %a@." pp_x msg Proc.Pid.pp
                    entry ~guard:(fun (from, x) -> x = B)
                      (fun (from, msg) ->
                         Fmt.epr "a: received %a from %a@." pp_x msg Proc.Pid.pp
          if not success then
            aux ()
        aux ()
  let b =
    Gateway.spawn (fun h ->
        Fmt.epr "b: my pid is %a@." Proc.Pid.pp (Proc.Handle.pid h);
        let _, send_to = recv_pid h in
        Fmt.epr "b: received instruction to send to %a@." Proc.Pid.pp send_to;

        let clock = Eio.Stdenv.clock (Proc.Handle.env h) in

        send_x h (send_to, C);
        send_x h (send_to, C);
        send_x h (send_to, C);
        send_x h (send_to, C);
        send_x h (send_to, C);
        send_x h (send_to, C);

        Eio.Time.sleep clock 5.0;

        send_x h (send_to, A);

        let from, msg = recv_x h in
        Fmt.epr "b: received %a from %a@." pp_x msg Proc.Pid.pp from;
  let _controller =
    Gateway.spawn (fun h ->
        Fmt.epr "controller: my pid is %a@." Proc.Pid.pp (Proc.Handle.pid h);
        send_pid h (a, b);
        Fmt.epr "controller: sent instructions to a@.";
        send_pid h (b, a);
        Fmt.epr "controller: sent instructions to b@.";
  Eio_main.run Gateway.main

Example output

  a: my pid is (0, 3)
  b: my pid is (0, 4)
  controller: my pid is (0, 5)
  a: received instruction to send to (0, 4)
  controller: sent instructions to a
  b: received instruction to send to (0, 3)
  controller: sent instructions to b
  a: I haven't received anything useful yet
  a: I haven't received anything useful yet
  a: I haven't received anything useful yet
  a: I haven't received anything useful yet
  b: received A from (0, 3)
  a: I haven't received anything useful yet
  a: received A from (0, 4)

cfgen preview release v1.0.0-alpha.0

Chris Armstrong announced

I’m happy to announce the first pre-release of cfgen, a library for writing AWS CloudFormation definitions in OCaml and generating working CloudFormation templates.

It is usable in its current form, but still under development. This release is to gather feedback and gauge community interest in its continued development.

Please see the tutorial and documentation to get an understanding of how it works and its current feature set.

You can currently install it directly from git using opam with the tag v1.0.0-alpha.0


Other OCaml News

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