Module Logs_lwt

Lwt logging.

The log functions of this module return Lwt threads that proceed only when the log operation is over, as defined by the current Logs.reporter.

See a cooperative reporter example.

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Log functions

type 'a log = ('aunit Lwt.t) Logs.msgf -> unit Lwt.t

The type for Lwt log functions. The returned thread only proceeds once the log operation is over. See Logs.log.

val msg : ?⁠src:Logs.src -> Logs.level -> 'a log

See Logs.msg.

val app : ?⁠src:Logs.src -> 'a log


val err : ?⁠src:Logs.src -> 'a log

See Logs.err.

val warn : ?⁠src:Logs.src -> 'a log

See Logs.warn.

val info : ?⁠src:Logs.src -> 'a log


val debug : ?⁠src:Logs.src -> 'a log

See Logs.debug.

val kmsg : (unit -> 'b Lwt.t) -> ?⁠src:Logs.src -> Logs.level -> ('a'b Lwt.t) Logs.msgf -> 'b Lwt.t

See Logs.kmsg.

Logging value Errors

val on_error : ?⁠src:Logs.src -> ?⁠level:Logs.level -> ?⁠header:string -> ?⁠tags:Logs.Tag.set -> pp:(Stdlib.Format.formatter -> 'b -> unit) -> use:('b -> 'a Lwt.t) -> ('a'b) Stdlib.result Lwt.t -> 'a Lwt.t

See Logs.on_error.

val on_error_msg : ?⁠src:Logs.src -> ?⁠level:Logs.level -> ?⁠header:string -> ?⁠tags:Logs.Tag.set -> use:(unit -> 'a Lwt.t) -> ('a[ `Msg of string ]) Stdlib.result Lwt.t -> 'a Lwt.t

See Logs.on_error_msg.

Source specific log functions

module type LOG = sig ... end
val src_log : Logs.src -> (module LOG)

src_log src is a set of logging functions for src.

Cooperative reporter example

The following reporter will play nice with Lwt's runtime, it will behave synchronously for the log functions of this module and asynchronously for those of the Logs module (see Note on synchronous logging).

It reuses Reporter and will produce colorful output if the standard formatters are setup to do so. For example it can be used instead of Reporter in the full setup example.

let lwt_reporter () =
  let buf_fmt ~like =
    let b = Buffer.create 512 in
    Fmt.with_buffer ~like b,
    fun () -> let m = Buffer.contents b in Buffer.reset b; m
  let app, app_flush = buf_fmt ~like:Fmt.stdout in
  let dst, dst_flush = buf_fmt ~like:Fmt.stderr in
  let reporter = Logs_fmt.reporter ~app ~dst () in
  let report src level ~over k msgf =
    let k () =
      let write () = match level with
      | Logs.App -> Lwt_io.write Lwt_io.stdout (app_flush ())
      | _ -> Lwt_io.write Lwt_io.stderr (dst_flush ())
      let unblock () = over (); Lwt.return_unit in
      Lwt.finalize write unblock |> Lwt.ignore_result;
      k ()
    in src level ~over:(fun () -> ()) k msgf;
  { = report }