[Caml-list] Attn: Development Editor, Latest OCaml Weekly News

Alan Schmitt
2022-06-07T10:16:06Z

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Hello

Here is the latest OCaml Weekly News, for the week of May 31 to June 07,
2022.

Table of Contents
─────────────────

carray.0.0.1
ML Family Workshop 2022: Final Call for Presentations
OCaml Users and Developers Workshop 2022
dkml-c-probe.2.0.0: Cross-compiler friendly definitions for C compiling
Full-Stack Web Dev in OCaml Tutorial w/ Dream, Bonsai, and GraphQL
Sketch.sh now supports multiple compiler versions, starting with 4.13.1
Explicit type binding and mutual recursion
findlib-1.9.4
omake-0.10.4
Old CWN

carray.0.0.1
════════════

Archive: <https://discuss.ocaml.org/t/ann-carray-0-0-1/9938/6>

Deep in this threas, Fabian said
────────────────────────────────

Note that you can, to a certain degree, build your own flat structures
with the `Bytes' module. Compared to bigarrays, `Bytes.t' has less
indirection, a lower constant memory overhead and can be allocated on
the minor heap. The contents of `Bytes.t' are not scanned by the GC,
just like bigarrays.

For example, a more efficient `int32 Array.t':

┌────
│ module Int32_array : sig
│ type t
│ val equal : t -> t -> bool
│ val create : int -> t
│ val length : t -> int
│ val get : t -> int -> int32
│ val set : t -> int -> int32 -> unit
│ val sub : t -> int -> int -> t
│ val to_list : bytes -> int32 list
│ end = struct
│ type t = Bytes.t
│ let equal = Bytes.equal
│ let create len = Bytes.create (4 * len)
│ let length t = Bytes.length t / 4
│ let get t i = Bytes.get_int32_le t (4 * i)
│ let set t i x = Bytes.set_int32_le t (4 * i) x
│ let sub t pos len = Bytes.sub t (4 * pos) (4 * len)
│ let to_list t = List.init (length t) (get t)
│ end
└────

A more efficient `(int * int)':

┌────
│ module Point : sig
│ type t
│ val create : int -> int -> t
│ val x : t -> int
│ val y : t -> int
│ end = struct
│ external get_int64_unsafe : bytes -> int -> int64 = "%caml_bytes_get64u"
│ external set_int64_unsafe : bytes -> int -> int64 -> unit = "%caml_bytes_set64u"
│ type t = Bytes.t
│ let create x y =
│ let p = Bytes.create 16 in
│ set_int64_unsafe p 0 (Int64.of_int x);
│ set_int64_unsafe p 8 (Int64.of_int y);
│ p
│ let x t = Int64.to_int (get_int64_unsafe t 0)
│ let y t = Int64.to_int (get_int64_unsafe t 8)
│ end
└────

(making a more efficient `(int * int) Array.t' is left as an exercise
to the reader)

The downside compared to bigarrays is that it doesn't support `sub'
without copying. Also, bytes can be moved by the GC (during minor GCs
or compaction), and therefore you cannot release the runtime lock when
passing them to C. The latter point is less relevant with the
multicore extensions, especially since there is no compactor
yet. There is some related discussion on the eio repository:
<https://github.com/ocaml-multicore/eio/issues/140>

ML Family Workshop 2022: Final Call for Presentations
═════════════════════════════════════════════════════

Archive:
<https://discuss.ocaml.org/t/ml-family-workshop-2022-final-call-for-presentations/9877/2>

Benoit Montagu announced
────────────────────────

ML Family Workshop 2022: DEADLINE EXTENSION
╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌

To increase your chances of submitting your work to the ML workshop,
*the submission deadline is extended by a week*. The new deadline is
Friday 10th June (AoE).

A quick reminder:
• The workshop does not have proceedings, making it the perfect venue
to run some ideas with the community or present some work in
progress within a friendly environment.
• The work load as an author is low: submissions are only 3 pages long
(excluding references)
• YOU have the power to make the ML workshop a success!
• You have one more full week to submit to
<https://ml2022.hotcrp.com/> (please register your submission
early!)
• All the details are here:
<https://icfp22.sigplan.org/home/mlfamilyworkshop-2022#Call-for-Presentations>
• The ML workshop is colocated with ICFP 2022
<https://icfp22.sigplan.org/>

OCaml Users and Developers Workshop 2022
════════════════════════════════════════

Archive:
<https://discuss.ocaml.org/t/ocaml-users-and-developers-workshop-2022/9726/4>

Matija Pretnar announced
────────────────────────

To offer additional opportunities to contribute to the OCaml workshop,
and to align with the [ML family workshop], to which you are also
cordially invited, the submission deadline has been extended by a week
to *Friday, June 10* (anywhere on Earth).

[ML family workshop]
<https://icfp22.sigplan.org/home/mlfamilyworkshop-2022#Call-for-Presentations>

dkml-c-probe.2.0.0: Cross-compiler friendly definitions for C compiling
═══════════════════════════════════════════════════════════════════════

Archive:
<https://discuss.ocaml.org/t/ann-dkml-c-probe-2-0-0-cross-compiler-friendly-definitions-for-c-compiling/9950/1>

jbeckford announced
───────────────────

Summary: dkml-c-probe is a new package for maintainers who compile or
link C code. Install it with `opam install dkml-c-probe'. Full docs
are at [https://github.com/diskuv/dkml-c-probe#readme]

[https://github.com/diskuv/dkml-c-probe#readme]
<https://github.com/diskuv/dkml-c-probe#readme>

Problem
╌╌╌╌╌╌╌

You are creating an OCaml package that has foreign C code. Perhaps you
need special C headers or libraries when you are targeting Apple
users, or perhaps you need to execute custom OCaml code for Android
users. More generally you need a way to determine whether your OCaml
or C code is compiling for a Linux AMD/Intel 64-bit, Android ARM
32-bit, or any other ABI target.

Solution
╌╌╌╌╌╌╌╌

A user of your OCaml package may, for example, be on a 64-bit
AMD/Intel Linux machine using a 32-bit OCaml system compiled with `gcc
-m32'; additionally they have a 32-bit Android ARM cross-compiler
toolchain. `dkml-c-probe' will tell you the target operating system is
`Linux' and the target ABI is `Linux_x86' except when the
cross-compiler toolchain is invoked. With the cross-compiler toolchain
`dkml-c-probe' will tell you the target operating system is `Android'
and the target ABI is `Android_arm32v7a'.

How it works
╌╌╌╌╌╌╌╌╌╌╌╌

`dkml-c-probe' uses C preprocessor definitions (ex. `#if
TARGET_CPU_X86_64', `#if __ANDROID__', etc.) to determine which ABI
the C compiler (ex. `ocamlopt -config | grep native_c_compiler') is
targeting.

This isn't a new idea. The pattern is used in Esy and Mirage code as
well. `dkml-c-probe' just codifies the pattern for use in your own
code.

Usage
╌╌╌╌╌

In OCaml code you can use the /versioned/ module:

┌────
│ module V2 :
│ sig
│ type t_os = Android | IOS | Linux | OSX | Windows
│ type t_abi =
│ Android_arm64v8a
│ | Android_arm32v7a
│ | Android_x86
│ | Android_x86_64
│ | Darwin_arm64
│ | Darwin_x86_64
│ | Linux_arm64
│ | Linux_arm32v6
│ | Linux_arm32v7
│ | Linux_x86_64
│ | Linux_x86
│ | Windows_x86_64
│ | Windows_x86
│ | Windows_arm64
│ | Windows_arm32
│ val get_os : (t_os, Rresult.R.msg) result Lazy.t
│ val get_abi : (t_abi, Rresult.R.msg) result Lazy.t
│ val get_abi_name : (string, Rresult.R.msg) result Lazy.t
│ end
└────

In C code you can use the [provided `dkml_compiler_probe.h' header]
from within Dune or Opam. Here is a snippet that handles part of the
Linux introspection:

┌────
│ #elif __linux__
│ # if __ANDROID__
│ # ...
│ # else
│ # define DKML_OS_NAME "Linux"
│ # define DKML_OS_Linux
│ # if __aarch64__
│ # define DKML_ABI "linux_arm64"
│ # define DKML_ABI_linux_arm64
│ # elif __arm__
│ # if defined(__ARM_ARCH_6__) || defined(__ARM_ARCH_6J__) ||
│ defined(__ARM_ARCH_6K__) || defined(__ARM_ARCH_6Z__) || defined(__ARM_ARCH_6ZK__) ||
│ defined(__ARM_ARCH_6T2__)
│ # define DKML_ABI "linux_arm32v6"
│ # define DKML_ABI_linux_arm32v6
│ # elif defined(__ARM_ARCH_7__) || defined(__ARM_ARCH_7A__) ||
│ defined(__ARM_ARCH_7R__) || defined(__ARM_ARCH_7M__) || defined(__ARM_ARCH_7S__)
│ # define DKML_ABI "linux_arm32v7"
│ # define DKML_ABI_linux_arm32v7
│ # endif /* __ARM_ARCH_6__ || ..., __ARM_ARCH_7__ || ... */
│ # elif __x86_64__
│ # define DKML_ABI "linux_x86_64"
│ # define DKML_ABI_linux_x86_64
│ # elif __i386__
│ # define DKML_ABI "linux_x86"
│ # define DKML_ABI_linux_x86
│ # elif defined(__ppc64__) || defined(__PPC64__)
│ # define DKML_ABI "linux_ppc64"
│ # define DKML_ABI_linux_ppc64
│ # elif __s390x__
│ # define DKML_ABI "linux_s390x"
│ # define DKML_ABI_linux_s390x
│ # endif /* __aarch64__, __arm__, __x86_64__, __i386__, __ppc64__ || __PPC64__,
│ __s390x__ */
└────

[provided `dkml_compiler_probe.h' header]
<https://github.com/diskuv/dkml-c-probe#c-header>

Versioning and Contributing
╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌

Whenever a new ABI is added, it goes into a new version (ex. `module
V3'). Your existing code that uses `module V2' will be unaffected.

But each new ABI needs to have its own maintainer because I don't have
access to every hardware platform on the planet!

For example, PowerPC (`ppc64') and Linux on IBM Z (`s390x') are
supported in the C Header but not the OCaml module because there are
no PowerPC and S390x maintainers.

Please consider contributing, especially if you want others to have an
easier compilation story for your favorite hardware platform.

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

Archive:
<https://discuss.ocaml.org/t/full-stack-web-dev-in-ocaml-tutorial-w-dream-bonsai-and-graphql/9963/1>

Alexander (Sasha) Skvortsov announced
─────────────────────────────────────

Hi everyone! I’ve written a tutorial blog series about full-stack web
development in OCaml, and wanted to share it here.

Last semester, I took Penn State's [CMPSC 431W], where our final
project was to build a database-driven web application. Since I'm
fairly familiar with web programming through my work on [Flarum] and
past internships/side projects, I decided to use this opportunity to
explore the OCaml web development ecosystem. I used [Dream] for the
backend, and [Bonsai] for the frontend.

While working on this project, I realized two things:

• OCaml is very underrated for web development. In addition to all the
language’s great features and safety guarantees, the ecosystem is
pretty good! Dream near-perfectly coincides with my vision of
backend webdev, and Bonsai has a great balance of
flexibility/elegance and safety.
• I couldn’t find realistic but accessible full-stack web projects in
OCaml available for reference. I found [tutorials] for [bits] and
[pieces], but nothing that connected all the dots.

I really enjoyed writing an article series on [hardware design with
OCaml], so I decided to do so for web development as well. In total, I
wrote 7 articles that walk through my project’s:

1. [Full-Stack WebDev in OCaml Intro]. This includes some background
on the project, and instructions for accessing the [live demo].
2. [Backend WebDev w/ Dream and Caqti].
3. [Building GraphQL APIs with Dream]
4. [Setting up Bonsai].
5. [Understanding Bonsai]. I actually wrote the first draft of this
before I decided to do a blog, while trying to, well, understand
Bonsai. It goes over some underlying concepts (SPAs, Frontend State
Management, Algebraic Effects, Monads), as well as Bonsai’s core
design.
6. [Using GraphQL in Bonsai].
7. [Routing in Bonsai and Project Conclusion].

Additionally, the [project’s README] has a comprehensive overview of
the tech stack, folder structure, and usage instructions. It also
includes some reflections on design decisions and my experience
working with these libraries.

I had a lot of fun writing these, and I hope they’re useful to anyone
considering OCaml for web development. Would be happy to answer any
questions or comments.

[CMPSC 431W]
<https://bulletins.psu.edu/university-course-descriptions/undergraduate/cmpsc/#:~:text=CMPSC%20431W%3A%20Database%20Management%20Systems>

[Flarum] <https://flarum.org/>

[Dream] <https://aantron.github.io/dream/>

[Bonsai] <https://github.com/janestreet/bonsai>

[tutorials] <https://github.com/paurkedal/ocaml-caqti>

[bits] <https://jsthomas.github.io/ocaml-dream-api.html>

[pieces]
<https://github.com/janestreet/bonsai/blob/master/docs/getting_started/counters.mdx>

[hardware design with OCaml]
<https://discuss.ocaml.org/t/hardcaml-mips-cpu-learning-project-and-blog/8088>

[Full-Stack WebDev in OCaml Intro]
<https://ceramichacker.com/blog/26-1x-full-stack-webdev-in-ocaml-intro>

[live demo] <https://cmpsc431.ceramichacker.com/>

[Backend WebDev w/ Dream and Caqti]
<https://ceramichacker.com/blog/28-2x-backend-webdev-w-dream-and-caqti>

[Building GraphQL APIs with Dream]
<https://ceramichacker.com/blog/29-3x-building-graphql-apis-with-dream>

[Setting up Bonsai]
<https://ceramichacker.com/blog/30-4x-setting-up-bonsai>

[Understanding Bonsai]
<https://ceramichacker.com/blog/31-5x-understanding-bonsai>

[Using GraphQL in Bonsai]
<https://ceramichacker.com/blog/32-6x-using-graphql-in-bonsai>

[Routing in Bonsai and Project Conclusion]
<https://ceramichacker.com/blog/33-77-routing-in-bonsai-and-project-conclusion>

[project’s README] <https://github.com/askvortsov1/nittany_market>

Alexander (Sasha) Skvortsov later added
───────────────────────────────────────

Also, forgot to mention this originally, but I recommend accessing the
demo with one of the emails from [this file] or [this file] (all
passwords are still [here]), as those users can also demo
create/update functionalities.

[this file]
<https://github.com/askvortsov1/nittany_market/blob/main/data/Local_Vendors.csv>

[this file]
<https://github.com/askvortsov1/nittany_market/blob/main/data/Sellers.csv>

[here]
<https://github.com/askvortsov1/nittany_market/blob/main/data/Users.csv>

Daniel Bünzli replied
─────────────────────

People who are looking for more lightweight alternatives – and want to
do web programming without bothering too much about front end insanity
can have a look at [hc] (yes indeed: sending HTML over `fetch', web
programming excels at running in circles).

The front JavaScript for that [CRUD webapp] comes out at 132Ko
uncompressed without even trying to tweak anything.

[hc] <https://erratique.ch/software/hc>

[CRUD webapp] <https://github.com/dbuenzli/hyperbib>

Sketch.sh now supports multiple compiler versions, starting with 4.13.1
═══════════════════════════════════════════════════════════════════════

Archive:
<https://discuss.ocaml.org/t/ann-sketch-sh-now-supports-multiple-compiler-versions-starting-with-4-13-1/9971/1>

Javier Chávarri announced
─────────────────────────

The interactive OCaml sketchbook [sketch.sh] has now support to store,
edit and run sketches in different versions of the OCaml compiler.

[sketch.sh] <https://sketch.sh/>

Support for 4.13
╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌

Storing and running sketches using the compiler version 4.13.1 is now
possible, this functionality has been added to the already existing
support for version 4.06.1. The Reason parser and formatting tool
refmt were also updated to a more recent version that supports 4.13.1.

Here you can see a sketch showcasing the monadic let syntax, using the
example from the official OCaml docs: [ZipSeq - Sketch.sh].

[ZipSeq - Sketch.sh] <https://sketch.sh/s/8cnNChTTq6IoGeFQarbvN2/>

Existing sketches and forks
╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌

Previously existing sketches remain in 4.06.1, while newly created
sketches will be on 4.13.1. For now, the only way to "migrate" a
sketch to the newer version of the compiler is by copying its content
and pasting it in a new sketch.

Forked sketches inherit the compiler version of the forked sketch.

Future plans
╌╌╌╌╌╌╌╌╌╌╌╌

In the future, there are plans to support version 4.14.0 of the
compiler, and we are considering adding a way so that the version of
the compiler can be chosen for a given sketch. We are also working on
migrating the editor UI codebase to a more recent version of
ReasonReact, and use JSX3 instead of JSX2.

Feature requests and bugs
╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌

Please [let us know] in case you have a feature request, or if you
encounter any issues or bugs. Also, don't hesitate to reach out via DM
or any other means if you would like to contribute or participate in
the project in some way.

Thanks to [Ahrefs] for supporting an Open Source Day initiative, which
allowed to allocate time to work on this improvement for sketch.sh,
and for providing the infrastructure to run the sketch.sh service for
the community. Thanks as well to the authors and maintainers of the
OCaml compiler, js_of_ocaml, and ReScript, that sketch.sh relies upon.

[let us know] <https://github.com/Sketch-sh/sketch-sh/issues/new>

[Ahrefs] <https://ahrefs.com/>

Explicit type binding and mutual recursion
══════════════════════════════════════════

Archive:
<https://discuss.ocaml.org/t/explicit-type-binding-and-mutual-recursion/9973/3>

Deep in this thread, octachron explained
────────────────────────────────────────

For most use cases, if you want an explicit annotation for recursive
function, it will be much simpler to use the `type a. ...' form:
┌────
│ let rec foo: type a. a -> a = fun x -> x
│ and bar: type a. a -> a = fun x -> foo x
└────
This form is a shortcut for both adding an explicit universal
quantified and and a corresponding locally abstract type (in other
words ~let f : 'a . …. = fun (type a) -> … ~).

The root issue with

┌────
│ let rec f (type a) (x:a) = f x
└────
is that the locally abstract type `a' is introduced after
`f'. Moreover, without an explicit type annotation, a recursive
function like `f' is monomorphic in its body and a monorphic function
cannot be called on a type that was defined after the function.

In other words, the issue is that in term of type scopes, the function
`f' is equivalent to
┌────
│ let f = ref Fun.id
│ type t = A
│ let x = !f A
└────
which also fails with
┌────
│ Error: This expression has type t but an expression was expected of type 'a
│ The type constructor t would escape its scope
└────
This is why the second solution proposed by @Gopiandcode
works. Indeed, in

┌────
│ let foo, bar = fun (type a) ->
│ let rec foo (x: a) : a = x
│ and bar (x: a) : a = foo x in
│ foo, bar
└────
the type `a' is defined before the recursive functions `foo' and
`bar', thus `foo a' does not break any scope constraint.

findlib-1.9.4
═════════════

Archive:
<https://sympa.inria.fr/sympa/arc/caml-list/2022-06/msg00004.html>

Gerd Stolpmann announced
────────────────────────

findlib-1.9.4 is out. It mainly includes a change in the configuration
script needed for OCaml-4-14.

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

<http://projects.camlcity.org/projects/findlib.html>

An updated OPAM package will follow soon.

omake-0.10.4
════════════

Archive:
<https://sympa.inria.fr/sympa/arc/caml-list/2022-06/msg00005.html>

Gerd Stolpmann announced
────────────────────────

I just released omake-0.10.4, the build utility. This finally includes
the fix for Apple Silicon, but also a couple of small changes (roughly
everything since PR#100 to PR#146 on GitHub).

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

Old CWN
═══════

If you happen to miss a CWN, you can [send me a message] and I'll mail
it to you, or go take a look at [the archive] or the [RSS feed of the
archives].

If you also wish to receive it every week by mail, you may subscribe
[online].

[Alan Schmitt]

[send me a message] <mailto:alan.schmitt@polytechnique.org>

[the archive] <https://alan.petitepomme.net/cwn/>

[RSS feed of the archives] <https://alan.petitepomme.net/cwn/cwn.rss>

[online] <http://lists.idyll.org/listinfo/caml-news-weekly/>

[Alan Schmitt] <https://alan.petitepomme.net/>

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