OCaml Weekly News

First I would like to announce the 1.9.0 minor release, see the release notes below for details.

There is also ongoing work in the caqti2 branch targeted for the next major release. If someone have an opinion on directions, we can discuss it here, or in the issue tracker (meta-issue), see my brief notes below.

I will attend parts of the ICFP 2022 virtually next week so there may be time to discuss over audio.

I, along with Jay, were the two Outreachy interns working with the OCaml :camel: community this summer. I worked on Multicore Applications and Jay on TopoJSON. Our internship, of course, was only made possible because @sudha and @patricoferris generously chose to volunteer to mentor us–as our respective mentors–throughout the summer. We are grateful to the both of them :heart:.

Our three-month long Outreachy internship just ended relatively recently and, personally, I have really enjoyed working on my project and learning OCaml. So much so that Jay and I would like to share our experiences with the rest of the community. :sparkles:

To carry forward a tradition established by the previous Outreachy cohort, we will host a virtual session that will consist of two short presentations from the both of us followed by a Q&A. The session will be on Friday 23rd September 2-3pm CET.

It is open to whoever wishes to join. A recording will be shared later online as well.

We hope you will join us! :raised_hands:

I suppose you mean CEST i.e. 2022-09-23T14:00:00+02:00/PT1H

Yes I do. Thank you for pointing it out.

I have an idea to build a SaaS for corporate blogging (like Medium, but for companies) and I want to try MirageOS as a total platform for services. I have no production experience with OCaml (only Golang, JS, Ruby) and have no experience with MirageOS and unikernels (only Docker, Linux, and a little bit k8s), but I’m very interested in both. Could you please help me to clarify possible issues with such an approach?

Also I’m interested about a hosting for MirageOS services. I don’t like containers and k8s stuff and I prefer dedicated and virtual servers instead of cloud stuff because I have no resources to pay up to 5x more for hosting.

Thank you for your help!

Thank you for your interest in MirageOS. MirageOS is first and foremost a framework for creating an application (such as a blog) for several targets. One of these targets is Solo5 which allows to create an entire system which includes everything necessary for OCaml (its runtime). Thus, one can deploy a MirageOS application on:

• KVM (with the target hvt)
• Xen
• or produce a simple executable taking advantage of seccomp (and thus finely controlling access to the executable).
• we can also mention the experimental target for Raspberry Pi 4

The objective of MirageOS is to make the choice of targets transparent to the application. This means that for a given application, deploying for KVM or Xen should not be an upstream choice (which would govern the development of the application) but the last of the choices which can, of course, be left to third party users.

This reverses the development logic of an application thanks to abstraction mechanisms (specific to OCaml) (the functors) that allow to get rid of any specialisation to a given system (Solo5, Unix, Raspberry Pi, etc.).

This is of course the theory and in practice, it works quite well :) .

To take the example of the blog, you can see Hannes’ blog or mine which runs on MirageOS (KVM). The latter have a similar architecture: a unikernel managing TLS certificates and redirecting HTTP connections to unikernels on a local network (tlstunnel or contruno) and a unikernel (unipi) that only transmits what appears in a Git repository via the HTTP protocol (http/1.1 and h2).

Deployment depends of course on what you have. Regarding KVM, you can follow the tutorials here (quite general) and there. You can deploy your unikernels on Google Cloud with this (probably a bit old) tutorial. Finally, a deployment with seccomp is possible, it is a simple executable.

Of course, most of these unikernels are already available for download here thanks to the excellent work of robur.io. It is ensured that the generated image is reproducible regardless of the context.

There is of course a whole series of unikernels made by the community that you can mainly find on GitHub. We can talk about several services like DNS or emails.

I would like to specify that all this is still experimental. We are gradually reaching the stage where our unikernels are used in production domains, but it still requires a lot of work and a lot of skills for such a small team :) . Of course, we are open to everyone’s participation and we are especially here to help newcomers.

I wrote up a longer form version of my setup at https://lambdafoo.com/posts/2022-09-07-ocaml-with-emacs-2022.html There are still some bits I am not happy with but I have been using it daily. Also @bbatsov wrote his version at https://batsov.com/articles/2022/08/23/setting-up-emacs-for-ocaml-development/

Imandra is looking for a full time engineer in the UK or in Austin, Texas.

The job offers can be found here.Imandra is an AI startup developing a cloud-native automated reasoning engine for analysis of algorithms and data. Whether you’re writing mission-critical code or need to understand the countless complex decisions that a system may make, use Imandra to ensure the algorithms you create are safe, explainable and fair. OCaml is the main language used at Imandra.

I am sure that the intersection of OCaml users and Acme users is small, but I have reason to believe it is a non-zero set :) . For those of you using this spartan editor, here are some plumbing rules that I use that allow me to right-click on error messages returned by the OCaml compilers, and jump to the referenced location in acme:

# example: in file "foo/bar.ml", line 155, characters 30-62
type	is	text
data	matches	'.*[Ff]ile "([^"]+)", line ([0-9]+), characters ([0-9]+)-([0-9]+).*'$nl'?'
arg	isfile	$1
data	set	$file
attr	add	addr=$2-#0+#$3,$2-#0+#$4
plumb	to	edit
plumb	client	$editor

# example: File "tests/dune", line 2, characters 7-22:
type	is	text
data	matches	'.*[Ff]ile "([^"]+)", lines ([0-9]+)-([0-9]+).*'$nl'?'
arg	isfile	$1
data	set	$file
attr	add	addr=$2,$3
plumb	to	edit
plumb	client	$editor

It could probably be extended to search ~/.opam so you could plumb errors in files outside of your project, but I do not use opam, so I haven’t needed to do it.

Here is a short demo of its use: https://youtu.be/Evl-N0oNNd0

It’s not in OCaml, but I also wrote https://github.com/droyo/acme-autoformat and put an OcamlFmt script in acme’s $PATH like so:

#!/bin/sh
exec /usr/local/bin/acme-autoformat -r '\.mli?$' \
	-- ocamlformat --name='{{.Basename}}' --enable-outside-detected-project -

This calls ocamlformat whenever I Put an .ml[i] file. This is probably obviated by combining acme-lsp and ocaml-lsp, but these two bits work well enough that I haven’t felt a need to pursue it.

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

• Tarides Sponsors Girls Can Code
• Introducing the Jane Street Graduate Research Fellowship