OCaml Weekly News

I'm very happy to announce the release of the Irmin 2.3.0 family of packages, including:

• irmin-pack.2.3.0, a storage backend for Irmin designed for and used by Tezos. This release contains a host of performance improvements as well as offline CLI features such as integrity checking. It also contains a number of high-level design changes, which were discussed in a recent Tarides blog post.

  Finally, irmin-pack.2.3.0 also contains a prototype of the layered irmin-pack store, which provides an OverlayFS-esque mode of operation for irmin-pack in which the causal history of the store can be chunked into independently-accessable substores. This feature will eventually be deployed in a future version of Tezos.

• irmin-containers, a collection of pre-defined mergeable data structures built using Irmin and compatible with any backend. These were originally provided by @kayceesrk as part of ezirmin, and has since been modernised and upstreamed by Anirudh S.
• irmin-bench, a suite of benchmarks for Irmin for use with current-bench, an experimental continuous benchmarking infrastructure for OCaml projects. Lots of work has been going on behind the scenes to make this a general benchmarking infrastructure for the Mirage ecosystem, including a recent fancy UI overhaul by new contributor @rizo.
• repr, an extraction of the Irmin.Type type representation library for use in other packages. This package contains a set of combinators for building run-time representations of types, along with various generic operations defined over those representations, including: equality, comparison, pretty-printing, JSON / binary codecs, etc. The API of this library is currently a work-in-progress, but we hope to use it more widely in the Mirage ecosystem soon.
• semaphore-compat, an extraction of the Semaphore library in OCaml 4.12, for libraries that want to maintain compatibility with earlier versions of OCaml.

The full list of changes to Irmin can be found here.

Many thanks to our open-source contributors and collaborators. Happy hacking!

On behalf of the dune, I'm pleased to announce the release of dune 2.8.0. This release contains many bug fixes, performance improvements, and interesting new features. I'll point out two new features that I'm most excited about.

First is the experimental dune_site extension that makes it possible to register and load plugins at runtime. This feature is quite involved, but we've documented it extensively in the manual.

Another cool feature is that we've eliminated the need for .merlin files and all the caveats that came with them. Now, merlin talks to dune directly to get precise configuration for every module. Say goodbye to all those "approximate .merlin file" warnings!

I encourage everyone to upgrade as soon as possible, as earlier versions are not compatible with OCaml 4.12. Happy Hacking.

Full change log:

On behalf of Nomadic Labs, I'm happy to announce the release of Lwt-canceler version 0.3. Lwt-canceler is a small library to help programs written using Lwt to synchronise promises around resource clean-up. This library was developed as part of the Tezos codebase before being released.

With this version, the code has matured significantly (including tests, documentation and some refactoring); the next release will probably be a version 1.0 at which point a more robust versioning scheme will be used.

The documentation is available online: https://nomadic-labs.gitlab.io/lwt-canceler/lwt-canceler/Lwt_canceler/index.html The code is released under MIT License and hosted on Gitlab: https://gitlab.com/nomadic-labs/lwt-canceler The new version is available on opam: opam install lwt-canceler

Happy hacking!

Let me share my new blog post on understanding format6 with examples. https://blog.tail.moe/2021/01/13/format6.html

It's almost my reading note for the paper Format Unraveled (on module Format) and experiments on utop. I tried not to be too verbose though.

Well, I made a sequel of format6 post, Understanding format6 in OCaml by diagrams https://blog.tail.moe/2021/01/15/format6-diagram.html

This time I just use four examples with four diagrams e.g. it's the one for Scanf.sscanf

p.s. It's a pity that I missed Gabriel's post The 6 parameters of (’a, ’b, ’c, ’d, ’e, ’f) format6 after writing that one.

The release of OCaml 4.12.0 is close.

The set of new features has been stabilized, and core opam packages already work with this release. After three alpha releases, we have created a first beta version to help you adapt your software to the new features ahead of the release. Compared to the last alpha, this beta contains only three new bug fixes and one change to the standard library.

The base compiler can be installed as an opam switch with the following commands

opam update
opam switch create 4.12.0~beta1 --repositories=default,beta=git+https://github.com/ocaml/ocaml-beta-repository.git

If you want to tweak the configuration of the compiler, you can pick configuration options with

opam update
opam switch create <switch_name> --packages=ocaml-variants.4.12.0~beta1+options,<option_list>
--repositories=default,beta=git+https://github.com/ocaml/ocaml-beta-repository.git

where <option_list> is a comma separated list of ocaml-option-* packages. For instance, for a flambda and afl enabled switch:

opam switch create 4.12.0~beta1+flambda+afl
--packages=ocaml-variants.4.12.0~beta1+options,ocaml-option-flambda,ocaml-option-afl
--repositories=default,beta=git+https://github.com/ocaml/ocaml-beta-repository.git

All available options can be listed with "opam search ocaml-option".

The source code is available at these addresses:

• https://github.com/ocaml/ocaml/archive/4.12.0-beta1.tar.gz
• https://caml.inria.fr/pub/distrib/ocaml-4.12/ocaml-4.12.0~beta1.tar.gz

If you want to test this version, you may want to install the alpha opam repository

https://github.com/kit-ty-kate/opam-alpha-repository

with

opam repo add alpha git://github.com/kit-ty-kate/opam-alpha-repository.git

This alpha repository contains various packages patched with fixes in the process of being upstreamed. Once the repository installed, these patched packages will take precedence over the non-patched version.

If you find any bugs, please report them here: https://github.com/ocaml/ocaml/issues

It's quite easy to get up to speed using the precompiled OPAM binary for macOS/ARM64.

• Download opam-2.0.7-arm64-macos.
• Move it to some directory in your PATH, rename it to opam, and make it executable. From a Terminal window:

mv ~/Downloads/opam-2.0.7-arm64-macos /usr/local/bin/opam
chmod +x /usr/local/bin/opam

• Try to execute it: opam init. You will be blocked by the macOS security checks, as the binary is not signed.
• Open Preferences / Security and Privacy. There should be a notice "opam was blocked because…" and an "Allow Anyway" button. Click on that button.
• Try again to execute opam init. You will be blocked again, but now there is an "Open" button. Click on that button. opam init should run and install the OCaml 4.10.2 compiler.
• From now on, you can run opam without being blocked. Use this freedom to opam install the packages you need.
• Some packages that depend on external C libraries may fail to install because these C libraries are not available. Normally we would rely on Homebrew or MacPorts to provide these C libraries, but these package collections are still being ported to macOS/ARM64.

As a reward for these minor inconveniences, you'll get excellent performance running OCaml software such as Coq. Single-core performance on a MacBook Air M1 is 20% better than the best x86 workstation I have access to.

@UnixJunkie will be speaking (virtually, of course) on OCaml Batteries Included at Houston Functional Programmers, this coming Wednesday, Jan 20 at 7pm (U.S. Central time). His talk will cover Batteries' history, place within the OCaml ecosystem, and comparisons with OCaml's other alternative standard libraries. All are welcome to join us, even if you're not from Houston. Complete details and Zoom info are at hfpug.org.

Here are links from many OCaml blogs aggregated at OCaml Planet.

• Coq 8.13.0 is out