OCaml Weekly News

Archive: https://framagit.org/brab/cwn

The editor announced:

Thanks to the hard work of Enzo Crance, we now have an OCaml-based tool to generate the OCaml weekly news. We now use Org mode for the conversion to html and text. Please don't hesitate to contact me for any bug report or suggestion.

Archive: https://discuss.ocaml.org/t/you-like-parmap-you-like-parany/2131/1

UnixJunkie announced:

So, here comes parpair: https://github.com/UnixJunkie/parpair

The ultimate step in minimalist parallel programming.

Of course, your function needs to be pretty heavy in order for the computation to be accelerated.

Archive: https://discuss.ocaml.org/t/ann-opam-check-all-are-your-packages-broken-for-the-upcoming-ocaml-releases/1875/28

Continuing this discussion, Kate announced:

The service now has a proper domain name: http://check.ocamllabs.io/

Archive: https://discuss.ocaml.org/t/ocaml-job-opportunity-at-citrix-in-cambridge-uk/2132/1

Christian Lindig announced:

The Citrix office in Cambridge develops the XenServer hypervisor which is open source and builds on Xen. The toolstack part of the product, which orchestrates the VMs, is developed in OCaml (see GitHub) and the team is looking for an engineer with strong affinity to functional programming in the Unix environment. Feel free to send me an email at christian.lindig@citrix.com with any questions. Below is the official job description.

https://jobs.citrix.com/job/CITRA005811517/Software-Engineer-Functional-Programming

Archive: https://sympa.inria.fr/sympa/arc/caml-list/2018-06/msg00020.html

Daniel Bünzli announced:

I'd like to announce omod which provides data-driven module toplevel loaders.

Like ocamlfind it allows to load compilation objects and their dependencies in the toplevel. However omod works without additional metadata files and with top level (compilation unit) module names rather than ocamlfind package or archive names.

This means you only need to know the name of the module you want to load rather than having to remember in which ocamlfind package or archive it lives.

It should work well in ocaml, ocamlnat[0] and utop. To get started type:

opam install omod

and follow the [tutorial][1]. More information on how omod came to be is given below [2].

omod is ISC licensed and can be found at http://erratique.ch/software/omod

Best,

Daniel

P.S. Currently omod doesn't work with opam system compilers.

[0] One issue with ocamlnat is that some libraries lack their cmxs files. E.g. the lack of threads.cmxs prevents the Core module from loading. But other ones like Irmin, Containers or Base do however load in ocamlnat via omod.

[1]: http://erratique.ch/software/omod/doc/Omod.html#tutorial

[2] This is basically a dependency-less rewrite of odig's toplevel loaders which will be removed from odig. It solves the following problems they had:

1. Too many dependencies. They brought too many dependencies in the toplevel including compiler-libs which are problematic in ocamlnat​. omod has no dependency, so using it limits toplevel scope pollution to the Omod module only which loads fine in ocamlnat.
2. Resolution for multiple load sequences. odig had no support for choosing between multiple load solutions (e.g. for library variants). omod has both a variant specification syntax and an interactive mode to resolve them.
3. Slow. They were too slow on large libraries as resolution was done in the (bytecode) toplevel itself, omod's performance (and API) should be improved for scripting however it is reasonably fast for your toplevel interactive usage.
4. Outdated information in long running toplevel sessions. They provided no mecanism to update the package information whenever the package install base changed.

To solve 1., 3. and 4. the Omod API invokes the omod binary with the load sub-command (whose textual output you can check when you suspect there's a problem) to find out the load sequences.

Archive: https://discuss.ocaml.org/t/tools-for-logic-programming-in-ocaml/2126/4

Continuing this thread from last week, th3rac said:

Also https://github.com/c-cube/datalog, a Datalog implementation

Archive: https://discuss.ocaml.org/t/ann-opam-ci-first-release-of-a-tool-to-check-the-health-of-your-packages/2146/1

Anil Madhavapeddy announced:

Cross posted from https://github.com/ocaml/infrastructure/wiki/Using-the-opam-ci-tool

Have you submitted a new opam package after testing it on your desktop, and then wondered if it builds on OpenSUSE or CentOS, or on an ARM or PowerPC architecture, or against a different version of the OCaml compiler, or if older version continues to work after a few years of being published? But you don't have the resources to check all these interactions manually, especially as the opam package database now contains thousands of revisions of OCaml source code. The new opam ci plugin comes to the rescue! The remainder of this post describes its uses, how to triage issues and then fix them.

opam-ci provides an interface to the opam2 continuous integration cluster, which regularly rebuilds the full package repository across a variety of OCaml compiler versions, operating system distributions and CPU architectures. These builds are done regularly in remote infrastructure and the results are pushed to a metadata repository where they are fetched by a CLI client to let you query the status of your packages.

• opam ci status shows a dashboard of the build results across this matrix. Packages can be filtered by maintainer substrings or tag names in the opam package description, so you see only those relevant to you.
• opam ci logs will show you the build errors so you can fix them. It also generates a Dockerfile of the precise build to reproduce the environment locally for you.

To get started, try these commands with the maintainer argument replaced with your own information or tags:

# show all the failing MirageOS packages
opam ci status -m org:mirage | less -R
# show all the packages maintained by anil@recoil.org
opam ci status -m anil@recoil.org --filter=all | less -R
# show all the packages failing on the latest RC of the OCaml compiler
opam ci status --filter=variants:rc | less -R
# display all failure logs for the mirage-xen package
opam ci logs mirage-xen

The status view shows a panel of icons that represent different combinations of ways to build opam packages. From left to right, these are:

• Compiler: The circled numbers represent OCaml compiler versions (a circled 6 is OCaml 4.06, a circled 7 is 4.07, and so on).
• Distro: The square letters indicate different OS distributions. D is Debian, F is Fedora, A is Alpine, U is Ubuntu and S is OpenSUSE.
• CPU Architecture: The small circled letters represent different CPU architectures. x represents x86_64, a is arm64 and p is PowerPC64LE.

Some compiler variants are also tested to track down specific problems, shown by the icons to the far right of the display. (see [below](#fix-specific-issues-around-ocaml-features) for more information on these).

• safe-string: The ss icon is for 'safe-string' failures, which would happen in OCaml 4.06 due to the switch to immutable strings.
• flambda: The fl icon is for packages that fail to compile with the flambda variant of the compiler.
• release-candidate: The flag icon is for packages that fail to compile with the latest release candidate of OCaml; this is useful to figure out how much of the ecosystem works with a soon-to-be-released compiler.

The colours indicate the result of the build: white indicates the package was not built due to constraints, green is a successful build, yellow indicates the build was skipped due to a dependency failure, red is a direct build failure of that package, and magenta and blue indicate package metadata errors such as a failure of the solver to find a solution or the package sources being unavailable. (note: colors are currently mandatory but this needs to be improved)

Archive: https://discuss.ocaml.org/t/does-ocaml-ecosystem-have-css-preprocessors/2139/3

Volodymyr Melnyk asked and Nadeem Bitar replied:

Does OCaml's ecosystem have CSS preprocessors except CCSS (cause I want to write CSS in OCaml)?

I've used bs-css to write CSS in OCaml.

It allows you to write something like:

open CSS
let card = style
[
  display flexBox;
  flexDirection column;
  boxShadow ~y:(px 3) ~blur:(px 5) (rgba 0 0 0 0 0.3);
]

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