Make the API a bit more regular reguarding formatters.

src/unix/Lwt_fmt.ml

@@ -31,6 +31,8 @@ let flush ppft = Format.pp_print_flush ppft.fmt () ; ppft.commit ()
 
 let make_formatter ~commit ~fmt () = { commit ; fmt }
 
+let get_formatter x = x.fmt
+
 (** Stream formatter *)
 
 type order =
@@ -80,9 +82,9 @@ let of_channel oc =
 (** Printing functions *)
 
 let kfprintf k ppft fmt =
-  Format.kfprintf (fun ppf -> k ppf @@ ppft.commit ()) ppft.fmt fmt
+  Format.kfprintf (fun _ppf -> k ppft @@ ppft.commit ()) ppft.fmt fmt
 let ikfprintf k ppft fmt =
-  Format.ikfprintf (fun ppf -> k ppf @@ Lwt.return_unit) ppft.fmt fmt
+  Format.ikfprintf (fun _ppf -> k ppft @@ Lwt.return_unit) ppft.fmt fmt
 
 let fprintf ppft fmt =
   kfprintf (fun _ t -> t) ppft fmt

src/unix/Lwt_fmt.mli

@@ -65,18 +65,24 @@ val make_formatter :
     functions to update the underlying channel.
 *)
 
+val get_formatter : formatter -> Format.formatter
+(** [get_formatter fmt] returns the underlying {!Format.formatter}. 
+    To access the underlying formatter during printing, it is
+    recommended to use [%t] and [%a].
+*)
+
 (** {2 Printing} *)
 
 val fprintf : formatter -> ('a, Format.formatter, unit, unit Lwt.t) format4 -> 'a
 
 val kfprintf :
-  (Format.formatter -> unit Lwt.t -> 'a) ->
+  (formatter -> unit Lwt.t -> 'a) ->
   formatter -> ('b, Format.formatter, unit, 'a) format4 -> 'b
 
 val ifprintf : formatter -> ('a, Format.formatter, unit, unit Lwt.t) format4 -> 'a
 
 val ikfprintf :
-  (Format.formatter -> unit Lwt.t -> 'a) ->
+  (formatter -> unit Lwt.t -> 'a) ->
   formatter -> ('b, Format.formatter, unit, 'a) format4 -> 'b
 
 val flush : formatter -> unit Lwt.t