About Lwt: concurrency library

Ecosystem
6

@alin, try using this program as a sample:

let () =
  Lwt_log_core.default :=
    Lwt_log.channel
      ~template:"$(date).$(milliseconds) [$(level)] $(message)"
      ~close_mode:`Keep
      ~channel:Lwt_io.stdout
      ();

  Lwt_log_core.add_rule "*" Lwt_log_core.Info;

  Lwt_main.run begin
    Lwt_log_core.info "blah"
  end

(* ocamlfind opt -linkpkg -package lwt.unix foo.ml && ./a.out *)

It produces output like this:

May 31 18:49:30.863 [info] blah

The Lwt_log docs are admittedly confusing, as they are split between two modules: Lwt_log_core and Lwt_log. This also got me once, because I last used Lwt_log heavily before it was split up like this.

In the program, I deliberately used Lwt_log_core for things that come from that module, so you can quickly find out what’s documented there, and what’s documented in Lwt_log. Lwt_log_core is actually included in Lwt_log, however, so normally one would just use Lwt_log to qualify all the identifiers.

EDIT: and thanks for asking. Another useful reminder to improve these docs :slight_smile:

EDIT 2: I also want to add that the template can be more elaborate when you are using a logger from Lwt_log, as you can see in the Lwt_log docs:

https://ocsigen.org/lwt/3.0.0/api/Lwt_log#VALrender