OCaml Weekly News

I'm pleased to mention that ppx_minidebug 2.0 is available now. The README at ppx_minidebug - GitHub is the user manual, and the runtime API is documented here: ppx_minidebug.Minidebug_runtime.

Version 2.0 brings linear verbosity log levels. Both logging scopes and individual log statements can be either: at a default (omitted) log level, at a compile-time log level (e.g. [%log2 "test"] logs test at level 2), or at a runtime-provided log level (e.g. [%logN for_level; "test"] logs test at level for_level). When the level to log at is omitted, it is inherited from its direct syntactic logging scope (i.e. the log entry that the log or log entry is syntactically in – not the log entry that the log is dynamically attached to, if it's different). Providing a compile-time log level will prune the generated code accordingly. See more here: ppx_minidebug: Using as a logging framework.

Version 1.6 brought support for local runtimes, where the runtime for logging in a logging scope is fetched by a user-provided function. The function can for example use domain-local storage. See more here: ppx_minidebug: Dealing with concurrent execution.

Happy debugging!

Over the past few weeks, I've started my journey to learn PPX, and during this process, I found it challenging to find examples. So, I began creating my own examples and adding explanations for myself.

I realized that I could make my examples and explanations public because this would push me to learn more deeply (as I’d need to provide better and clearer explanations) and could also help anyone else on this learning path. @davesnx also encouraged me to share my process (maybe through a blog post in the future). So, I created this repository: github.com/pedrobslisboa/ppx-by-example.

The idea is to have examples and an explanation for each detail on those. It has also a brief explanation about the subject on every README.

I have a few notes:

• It is a wip project, which means that there are parts in development. But sharing it is also a way to push me to improve this project.
• As I said, I'm on the process of learning PPX, so probably I missed or added something wrongly, so please If you notice it, share it on the repo so I can fix.
• I am also in the process of learning OCaml. I started coding in OCaml this year (professionally just last month), so this repository might not have the best code. If you think it can be improved, please let me know. :heart:
• I'm not a native English speaker or the best writer. I asked ChatGPT to help fix some mistakes and improve cohesion, but if you notice anything that needs to be improved, please let me know. :heart:

Besides that, any comments, help, or additions are welcome. I hope this can be helpful :3 Thank you all!

My favourite example at the moment is this one from Retrofitting Effect Handlers onto OCaml. It shows OCaml calling C, C calling an OCaml callback and exceptions crossing those boundaries.

$ cat meander.ml

external ocaml_to_c
         : unit -> int = "ocaml_to_c"
exception E1
exception E2
let c_to_ocaml () = raise E1
let _ = Callback.register
          "c_to_ocaml" c_to_ocaml
let omain () =
  try (* h1 *)
    try (* h2 *) ocaml_to_c ()
    with E2 -> 0
  with E1 -> 42
let _ = assert (omain () = 42)

$ cat meander_c.c

#include <caml/mlvalues.h>
#include <caml/callback.h>

value ocaml_to_c (value unit) {
    caml_callback(*caml_named_value
                  ("c_to_ocaml"), Val_unit);
    return Val_int(0);
}

Compile it with OCaml 5.2:

$ ocamlopt --version
5.2.0
$ ocamlopt meander_c.c meander.ml -o meander.exe
$ ./meander.exe
$ echo $?
0

Bonus you can use GDB/LLDB on this to set breakpoints in both OCaml and C.

With the conclusion of the previous Outreachy round (see Outreachy Demo Presentation), the next round is fast approaching and the OCaml community has signed up again to participate!

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

• The Biggest Functional Programming Conference of the Year: What are we Bringing to ICFP?
• ICFP 2024
• Project-Wide Occurrences: A New Navigation Feature for OCaml 5.2 Users
• What the interns have wrought, 2024 edition