OCaml Weekly News

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Here is the latest OCaml Weekly News, for the week of April 28 to May 05, 2020.

Table of Contents

Lwt now has let* syntax

Anton Bachin announced

Lwt now has let* and let+ syntax, which can be used like this:

open Lwt.Syntax

let () =
  let request =
    let* addresses = Lwt_unix.getaddrinfo "google.com" "80" [] in
    let google = Lwt_unix.((List.hd addresses).ai_addr) in

    Lwt_io.(with_connection google (fun (incoming, outgoing) ->
      let* () = write outgoing "GET / HTTP/1.1\r\n" in
      let* () = write outgoing "Connection: close\r\n\r\n" in
      let* response = read incoming in
      Lwt.return (Some response)))

  let timeout =
    let* () = Lwt_unix.sleep 5. in
    Lwt.return None

  match Lwt_main.run (Lwt.pick [request; timeout]) with
  | Some response -> print_string response
  | None -> prerr_endline "Request timed out"; exit 1

This is now released in Lwt 5.3.0. Thanks to Rahul Kumar for adding let*, and @CraigFe for adding let+!

Thomas Coopman asked

Awesome this looks great.

2 quick questions:

  1. I don't see this new version documented on ocsigen yet? Is that a build that needs to be done manually?
  2. Is ppx_lwt still recommend for some usecases like try%? For what cases is one preferred over the other?

Anton Bachin replied

Good questions :slight_smile:

  1. The docs generation is blocked on an Ocsigen "internal" package wikidoc, which has not been updated to support 4.08. So, effectively, let* is exactly what is preventing docs generation for the time being. I'll post the docs as soon as that is fixed.
  2. ppx_lwt is probably still the recommended way, because of better backtraces, and things like try%lwt. let* is nice for people that don't want to use the PPX. They can still benefit from a monadic syntax.

JOSE 0.3.0 - Now with 100% more encryption

Ulrik Strid announced

I recently released a version 0.3.0 of JOSE.


It now includes some of the JWE (JSON Web Encryption) spec. A huge thank you goes out to @hannes for helping me implementing one of the gnarlier combinations of decryption that I could then use as a base for encryption and more alg and enc.

I also refactored the JWK (JSON Web Keys) implementation to unify and simplify the representation. It is now possible to use a private key for anything a public key can do since it's a superset.

A special thanks to @anmonteiro for helping me with the design and reviewing my code.

Are there learning materials for OCaml for those with no programming experience?

Aaron Christianson asked

OCaml is a language with some advanced features, but a very gentle learning curve. It seems like it would be well-suited to teaching beginners to program (a few tricky error messages notwithstanding), but I haven't seen many resources targeted at teaching programming from scratch. Does anyone here know any?

Daniel Bünzli replied

There is OCaml from the Very Beginning written by @JohnWhitington.

Nicolás Ojeda Bär also replied

An excellent (free) book is "LE LANGAGE CAML" https://caml.inria.fr/pub/distrib/books/llc.pdf.

Pierre also replied

There's also CS3110 from Cornell University. Here's the textbook. It's pretty great!

The recent evolution of utop, lambda-term, zed and underneath projects

ZAN DoYe announced

Hi, dear OCaml guys! We've been keeping quiet for more than one year though utop, lambda-term, zed and some related projects were still evolving during the period of time. This is because of two reasons:

  1. The new feature had nothing to do with the fields where most OCaml developers are working on:



    Recognizing, editing, fuzzy searching for Character Variation(mainly for ancient CJK characters).

    Nevertheless, the new feature brought us a good side effect – the long-existing Issue with asian charset was resolved. UTop users will notice the refinement naturally, so no announcement was needed.

  2. I didn't deem the first few new editions of zed 2 and lambda-term 2 stable enough.

3.0 era

This time, we are entering zed 3, lambda-term 3 era. The features introduced since zed 2, lambda-term 2 are quite stable now and the new feature coming to us will have a bit more impact, especially to vim users. So it's worthwhile to draft an announcement:

  • VI Editing Mode


    OCaml guys, hope you enjoy this.

List of notable changes:

  • zed 2:
    • wide, combined glyph(Character Variation, IPA, CJK …)
    • add wanted_column support for wide width character
  • lambda-term 2:
    • wide, combined glyph(Character Variation, IPA, CJK …)
    • add horizontal scrolling support for wide width character
  • zed 3:
    • add new actions for convenience
  • lambda-term 3:
    • LTerm_read_line: add initial support for vi editing mode:
    • motions:
      • h l 0 ^ $
      • j k gg G
      • w W e E b B ge gE
      • f F t T
      • aw iw aW iW
      • include or inner ( ), [ ], { }, < >, ' and "
      • generic quote: aq? iq? where ? could be any character
      • bracket matching: jump back and forth between matched brackets
    • delete, change, yank with motions
    • paste: p P
    • line joining: J

for a full list of the changes, please visit the homepages of each project.

Projects underneath:

  • charInfo_width: Determine column width for a character
  • mew & mew_vi: Modal editing witch & Its VI interpreter complement. In a word, modal editing engine generators.

What's next

  • VI Editing Mode
    1. Visual mode


    2. register support and more vi compatible
  • CJKV

    We've recorded more then 100 thousand entries about the structure of CJK characters, what is a character consists of, how are the sub-assemblies glue together etc. And as a complement to charInfo_width, we may release a new project called charInfo_structure ;)

Looking for "lovely, idiomatic" examples of Ocaml used for shell-scripting in the manner of Perl/Python (but esp. Perl)

Chet Murthy announced

I wonder if there are people who have written nontrivial Ocaml code for shell-scripting, that they think exemplifies the right way to do it. I've been a Perl hacker for 25yr, and so when I reach for Ocaml to write stuff that should be Perl shell-scripts, I always find it a bit painful, and there's a significant overhead to getting the job done. Some of that is applying ocaml to a new domain, but some of it is that I'm just not using the right idioms and tools (and there are so many to choose from).

So if anybody has good pointers, I'd appreciate learning about them.

Bikal Lem

Haven't tried it myself, but this looks promising … https://github.com/janestreet/shexp.

At least it has the great Sean Connery in its README so possibly worth delving a bit. :)

Hezekiah Carty

bos seems like it can do a lot of what you're looking for. It's at least worth taking a look, though it may not be at Perl levels of concise for this kind of task.

Martin Jambon

I tried to summarize my take on the subject into this gist: https://gist.github.com/mjambon/bb07b24f89fa60c973735307ce9c6cb9

I'm not aware of the existence of such tool, but this is how I might design it. This should be reminiscent of camlp4's quotation and anti-quotation system, which allows alternating between two syntaxes within a source file.


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