OCaml Weekly News

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Here is the latest OCaml Weekly News, for the week of June 07 to 14, 2022.

Table of Contents

Lwt informal user survey

Continuing this thread, Raphaël Proust said

Thanks to everyone who took the time to answer the polls above. I've now closed them.

The first pull-request to come out of this poll is [https://github.com/ocsigen/lwt/pull/947](removing support for OCaml<=4.07). This was the cutoff in the poll. It removes a lot of #if preprocessing statements and a few workarounds to stay compatible with old Stdlib interfaces. Thanks to @hannes for contributing most of the commits on this pull-request. If support for OCaml<=4.07 is important to you, please participate in the pull-request's discussion or on this thread.

Stay tuned for more. (But also be patient.)

Tutorial: Full-Stack Web Dev in OCaml w/ Dream, Bonsai, and GraphQL

Continuing this thread, jerben asked and Daniel Bünzli replied

Very interesting, did you write somewhere about how it compares to htmx?

Not really.

As far as I can remember I liked the ideas but found their execution to be a bit lacking, sometimes ad-hoc in their attribute DSL, focusing more on the show off to convince single page application proponents of the approach than on a clear conceptual model (which hc tries to detail in the manual here).

Two other things that come to mind are:

  1. AFAIR their examples relied a lot on unique id attributes for targeting request results. Unless you find a principled and automated way to generate these that's not compositional and brittle. In hc I extended the CSS selector syntax to allow to address your ancestors (peace be upon them). That's more compositional but now you become sensitive to structural changes in your markup – pick your poison[^1].
  2. I'm no longer sure about that, i.e. don't take my word for it, but I think their DSL allowed to spread the definition of an interaction among many elements which made it more difficult to understand what is happening. In hc all attributes defining the effects of an interaction are always located on a single element, the element that performs the request.

Finally when things go wrong I prefer to have to understand 700 lines of ml rather than 2800 lines of JavaScript (note that they likely have better legacy browser support and more functionality).

In any case there's a long list of todos in hc and it likely needs one or two more design rounds before getting to something decent – if that's even remotely possible on the web.

Dang it @dbuenzli one day you’ll run out of letters and need to come up with an actual name for your libraries.

Mind you I tried to use three letters once, but the whole experience turned out to be extremely unpleasant :–)

[^1]: Using unique ids reifed in an OCaml EDSL could be a better idea.

dkml-c-probe: Cross-compiler friendly definitions for C compiling

jbeckford announced

V3 is available. Its C_abi module has some big enhancements:

  • cleaner API (thanks @mseri!)
  • recognizes the BSD family: OpenBSD, FreeBSD, NetBSD and DragonFly on x86_64 hardware
  • integration testing now includes OpenBSD, FreeBSD and one cross-compiling toolchain (macOS x86_64 host that targets arm64)

V3 also has a new module C_conf which occupies the same problem space as findlib / ocamlfind and pkg-config:

  • Unlike findlib which is a specification+tool for 3rd party OCaml libraries, C_conf is a specification+tool for foreign C libraries
  • Unlike pkg-config which is a specification+tool for system (host ABI) C libraries, C_conf is a specification+tool for the multiple ABIs that are present when you cross-compile OCaml or C code
  • Unlike pkg-config which is designed for Unix, C_conf is designed for Windows and Unix where paths may have spaces, backslashes and colons
  • For now the specification is based on environment variables. If it proves useful the specification can be extended.

Examples and doc links for V3 are available at https://github.com/diskuv/dkml-c-probe#dkml-c-probe

Marcello Seri asked and jbeckford replied

Thanks a lot for the update! Can you say a bit more about how C_conf works?

C_conf has a detailed problem statement and spec at https://diskuv.github.io/dkml-c-probe/dkml-c-probe/Dkml_c_probe/C_conf/index.html (which is linked to on the dkml-c-probe README).

I probably shouldn't regurgitate the doc here, so I'll take a few key pieces from the doc and then post some things here that I didn't put on that doc page …

  1. Here is my configuration for locating the "gmp" library on my Apple Silicon host machine that cross-compiles to x86_64:

    CP_GMP_CC_DEFAULT                 = -IZ:/build/darwin_arm64/vcpkg_installed/arm64-osx/include
    CP_GMP_CC_DEFAULT_DARWIN_X86_64   = -IZ:/build/darwin_x86_64/vcpkg_installed/x64-osx/include
    CP_GMP_LINK_DEFAULT               = -LZ:/build/darwin_arm64/vcpkg_installed/arm64-osx/lib;-lgmp
    CP_GMP_LINK_DEFAULT_DARWIN_X86_64 = -LZ:/build/darwin_x86_64/vcpkg_installed/x64-osx/lib;-lgmp
    • The other direction may be more interesting, since the free GitHub Actions only supports x86_64. The scenario of taking a macOS x86_64 GitHub host and cross-compiling to Apple Silicon is implemented and partially tested.
  2. I am using a C package manager (vcpkg) to give me cross-compiled libraries and the flags for the target ABI (in this case darwin_x86_64 is the target ABI). In general it doesn't matter where you get your target ABI compatible libraries from. Example: When I'm cross-compiling to Android on a Windows x86_64 host, the Android Studio environment gives me some libraries for an Android Emulator (host ABI) and also prebuilt libraries for 4 Android device ABIs:

    Directory: C:\Users\xxx\AppData\Local\Android\Sdk\ndk\23.1.7779620\prebuilt
    Mode                 LastWriteTime         Length Name
    ----                 -------------         ------ ----
    d-----        10/20/2021   8:27 PM                android-arm
    d-----        10/20/2021   8:27 PM                android-arm64
    d-----        10/20/2021   8:27 PM                android-x86
    d-----        10/20/2021   8:26 PM                android-x86_64
    d-----        10/20/2021   8:27 PM                windows-x86_64
  3. The CP_clibrary_CC_DEFAULT_abi configuration relies on abi (the ocamlfind toolchain name) being standardized. The gmp library, for example, is used by many OCaml packages; I wanted one configuration for gmp, not one configuration for each (gmp, OCaml package) combination. In fact, getting a consistent abi naming was one of my motivations for releasing dkml-c-probe. I don't think the prior art got this right … the very stale opam-cross-android project uses abi = "android" which is insufficient to differentiate the 5+ sets of libraries available in Android Studio.
  4. The "gmp" (etc.) configuration is done once in a familiar syntax (-L, -I, -l). However the C_conf library will parse and print the configuration in the appropriate C compiler syntax. When the MSVC compiler is used you get MSVC style linking:


    MSVC and GCC conventions are supported today in C_conf.

  5. A real example of using C_conf is in my customization of zarith library. It checks C_conf first to see whether the user has the host/target ABI configuration; if it doesn't it falls back to pkg-config.

The trend of using pkg-config in OCaml packages makes both native Windows and cross-compilation difficult. At the moment we unintentionally shoot ourselves in the foot because Dune documentation encourages pkg-config for understandable reasons. I hope dkml-c-probe can break that trend.

Htmx/hc web development approach

Vladimir Keleshev announced asked

@cemerick, @yawaramin, @dbuenzli, and others who've used htmx/hc with OCaml back-end: what is your experience with templating? It seems that htmx/hc puts high requirements on a flexible HTML templating/DSL. What did you choose and is it working out for you?

Daniel Bünzli replied

I'm using OCaml and an absolutely trivial HTML generation library. If you want to see a real world example head to the *_html.{ml,mli} files in this directory (more on the structure found there here)

Works quite well for me but I'd say the problem is not really templating it's rather non-brittle URL management. For that I use this module which while I'm not entirely convinced by it yet, allows me to type them and avoid the stringly unchecked dependendencies so characteristic of the web development world.

Chas Emerick also replied

Yeah, you're right on that point.

I'm using tyxml for 99% of my HTML generation, specifically its jsx ppx. I am judicious about keeping the main logics of the project in OCaml proper; .re files exist exclusively to hold markup. The end result is a very pleasant environment IMO. In the end, I dearly wish there was a way to get actual HTML syntax into .ml files (I am no fan of reason syntax outside of jsx, and I suspect the sorta-legacy jsx toolchain leftover from reasonml will end up being a tech risk over time), but as things stand, it's the best option I've found.

Yawar Amin also replied

I'm just using Dream's 'built-in' templating, 'Embedded ML (.eml)', it works reasonably well–each template or partial is just a function that you define to take some arguments and return some markup. It even auto-escapes to prevent injection attacks. E.g.,

let card name =
  <div class="card"><%s name %></div>

There are a couple of tricks to be aware of with the EML syntax but in general it works well.

Simon Cruanes also replied

For the little webdev I do (internal tools mostly for myself), I've also been using server side html generation, with my own wheels tools and a bit of htmx.

Here's an excerpt from a personal project, with my own httpd and html combinators; it adds a root to handle /thy/<some string>:

let h_thy (self:state) : unit =
  H.add_route_handler self.server
    H.Route.(exact "thy" @/ string_urlencoded @/ return) @@ fun thy_name req ->
  let@ () = top_wrap_ req in
  let thy = Idx.find_thy self.st.idx thy_name in
  let res =
    let open Html in
      div[cls "container"][
        h3[][txtf "Theory %s" thy_name];
        Thy_file.to_html thy;
        div [
          "hx-trigger", "load";
          "hx-get", (spf "/eval/%s" @@ H.Util.percent_encode thy_name);
          "hx-swap", "innerHtml"] [
          span[cls "htmx-indicator"; A.id "ind"][
            txt "[evaluating…]";
  reply_page ~title:(spf "theory %s" thy_name) req res

Engineer and postdoc positions in France (various labs) to work on a proof assistant for crypto protocols

David Baelde announced

We are looking for engineers and postdocs to work on Squirrel, a proof assistant dedicated to proving cryptographic protocols. We have a broad range of projects in mind, ranging from pure OCaml development to involved protocol formalizations, with several theoretical questions in between. If you'd like to work on some of these aspects for one or more years, please get in touch with us!

More details can be found here:


Yojson 2.0.0

Marek Kubica announced

This Friday, it is my pleasure to announce the release of Yojson 2.0.0. You can get it in your local OPAM repository.

Key highlights include:

  • Fewer dependencies: Given Yojson is a common dependency we cut down on its dependencies so you have to install less and have less transitive dependencies
  • Seq interface: Since OCaml 4.14 deprecates Stream and 5.0 removes it, this was a good time to change to this interface
  • Buffer interface: coming along with #1, we changed Yojson to use Buffer wherever it was using Biniou types before

Thanks to everybody involved in this release!

If Yojson sounds like an interesting project for you to contribute, join us.

Full changelog follows:



  • Removed dependency on easy-format and removed pretty_format from Yojson, Yojson.Basic, Yojson.Safe and Yojson.Raw. (@c-cube, #90)
  • Removed dependency on biniou, simplifying the chain of dependencies. This changes some APIs:

    • Bi_outbuf.t in signatures is replaced with Buffer.t
    • to_outbuf becomes to_buffer and stream_to_outbuf becomes stream_to_buffer

    (@Leonidas, #74, and @gasche, #132)

  • Removed yojson-biniou library
  • Removed deprecated json type aliasing type t which has been available since 1.6.0 (@Leonidas, #100).
  • Removed json_max type (@Leonidas, #103)
  • Removed constraint that the "root" value being rendered (via either pretty_print or to_string) must be an object or array. (@cemerick, #121)
  • Removed validate_json as it only made sense if the type was called json. (@Leonidas, #137)
  • Add an opam package yojson-bench to deal with benchmarks dependency (@tmcgilchrist, #117)
  • Add a benchmark to judge the respective performance of providing a buffer vs letting Yojson create an internal (#134, @Leonidas)
  • Add an optional suf keyword argument was added to functions that write serialized JSON, thus allowing NDJSON output. Most functions default to not adding any suffix except for to_file (#124, @panglesd) and functions writing sequences of values where the default is \n (#135, @Leonidas)
  • The stream_from_* and stream_to_* functions now use a Seq.t instead of a Stream.t, and they are renamed into seq_from_* and seq_to_* (@gasche, #131).
  • Avoid copying unnecessarily large amounts of strings when parsing (#85, #108, @Leonidas)
  • Fix stream_to_file (#133, @tcoopman and @gasche)

opentelemetry 0.2

Simon Cruanes announced

It is my pleasure to announce the release of ocaml-opentelemetry 0.2. This library provides a core instrumentation library, as well as exporters, for the opentelemetry standard for observability; it encompasses distributed tracing, metrics, and (more recently) log export. A lot of tools are compatible with opentelemetry these days, including Grafana, DataDog, jaeger, etc.

This is still very early days for ocaml-opentelemetry, feedback and contributions are welcome.


Gerd Stolpmann announced

I just released omake-0.10.5, the build utility, which fixes the broken installation of version 0.10.4 from last week.

For docs and the download link see http://projects.camlcity.org/projects/omake.html. opam is underway.


Gerd Stolpmann announced

findlib-1.9.5 is out, fixing some scripting errors in the version 1.9.4 from last week.

For manual, download, manuals, etc. see here:


An updated OPAM package will follow soon.


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