OCaml Weekly News

A couple of notes on Marshal, which I don't think have been covered

• Although the guarantee is only between identical versions of OCaml, the implementation actually goes to considerable lengths to maintain backwards compatibility (so a value written by older OCaml remains readable in newer OCaml). Our own testsuite, for example, indirectly includes a test which unmarshals a 3.12.1 value. I don't know exactly how far back the support goes.
• As it happens, the change which affected Unison in 4.08 was the first breaking change to Marshal since either 4.00 or 4.01. The fact that it doesn't break often (and that the two code paths - at least at present - are small) meant I have suggested a few months back that we could in future add an additional flag in the style of Compat_32 to allow values to be written in a way which should be readable on older versions of OCaml. Indeed, it's small enough that flags could be added for the changes in 4.08 (PR#1683) and in 4.11 (PR#8791).
• Neither point undermines using alternative formats either for network serialisation or persistent storage, for the many reasons discussed above!

I am a great fan of Menhir, and have used it in several private language projects, using the ulexing scanner generator to provide Unicode-capable scanners.

Alarmed by the obsolescence of ulexing, and needing a utf8-capable scanner in a hurry I decided to (teach myself to) use Sedlex. On the whole the experience was very satisfactory, and I found it straightforward to produce a variant of the sedlexing library which supports buffers with variable chunk sizes, thereby enabling efficient lexing on channels connected to files as well as immediately responsive lexing on channels connected to terminals.

I also wanted to teach myself how to use the error-reporting, incremental, interfaces to Menhir-generated parsers. In the hope that it might be useful to others facing the same learning task, or the problem of adapting Sedlex for efficient interactive use, I have placed the example mock-S-Expression parser that resulted from this excursion in:

Git Repository: github.com/sufrin/InteractiveSedlexMenhirExample

I'm happy to announce that awa-ssh (https://github.com/mirage/awa-ssh) has just been merged into opam-repository. It is a pure OCaml implementation of the ssh (secure shell, https://en.wikipedia.org/wiki/SSH_(Secure_Shell)) protocol.

This is the initial release, please report issues you encounter.

It was initially developed by Christiano Haesbaert in 2016, and revived mid-2019 by myself and in 2020 it was migrated to the MirageOS organization on GitHub for further development and maintenance.

Both client and server code are present in the library (pure code in the main awa package), though the awa-lwt package implements only a server, and the awa-mirage package implements only a client. Tests and examples are in the test subdirectory.

The MirageOS client has been successfully used to clone git repositories (on private servers, on GitHub, etc.). It supports apart from RSA keys also ED25519 keys (and key exchanges).

I wrote a shell scripting library called Feather. I like idea of writing bash-like code quickly, later being able to intersperse OCaml to add more typeful components as needed. It's kind of like Shexp but without the monadic interface and with Async support. (Feather_async)

There's a tutorial and some examples in the link above but here's a quick taste:

open Feather

let lines = find "." ~name:"*.ml"
  |. tr "/" "\n"
  |. map_lines ~f:String.capitalize
  |. sort
  |. process "uniq" [ "-c" ]
  |. process "sort" [ "-n" ]
  |. tail 4
  |> collect_lines
in
String.concat ~sep:", " lines |> print_endline

Let me know if you have any feedback! And feel free to file bug reports here. Hope it ends up being useful, entertaining, or both!

We are looking for postdoctoral researchers and postdoctoral or postgraduate research engineers to help develop semantics and verification to improve the foundations and security of mainstream computer systems, for CHERI and Arm system software verification, at the University of Cambridge. OCaml expertise to help develop verification tools will be especially welcome. Closing date 13 January 2021 - see the advert http://www.jobs.cam.ac.uk/job/28012/.

A few days ago, I released ocb. It's a library and a command-line tool to generate SVG badges.

To get started quickly:

ocb --label Hello --color green --style flat --labelcolor white --status Goodbye

Will gives this result: SVG example.

My first use case was To.ml where I'm using bisect_ppx to generate and deploy a coverage report. I wanted to display the coverage percentage in the README and tried existing tools but wasn't fully satisfied as they didn't work or were failing randomly. Now, I'm generating the badge directly in a GitHub action.

The project was inspired by badgen. I still have to add support for icons and to improve the documentation but it's usable.

We, the ocaml-git team, are happy to announce a new major release of ocaml-git v3.0 and related libraries.

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

• How We Lost at The Delphi Oracle Challenge
• Tarides sponsors the Oxbridge Women in Computer Science Conference 2020
• Coq 8.12.2 is out
• First release of MetAcsl plugin
• Announcing MirageOS 3.10
• ReScript 8.4
• Coq 8.13+beta1 is out