error.txt

ocamlfind ocamlopt -package unix,extlib,dynlink,lwt.unix,core,curl,xml-light -thread -shared -o plugins/weather.cmxs plugins.ml plugins/weather.ml
File "plugins/weather.ml", line 60, characters 26-164:
Error: Signature mismatch:
       ...
       Values do not match:
         val handle_privmsg :
           < writef : string -> 'a -> string -> 'b; .. > ->
           'a -> string -> 'b
       is not included in
         val handle_privmsg : #Plugins.bot -> string -> string -> unit Lwt.t
       File "plugins/weather.ml", line 62, characters 8-22:
         Actual declaration

plugins.ml

open Lwt

class type bot = object
    method writef : 'a. ('a, unit, string, unit Lwt.t) format4 -> 'a
end

module type Plugin = sig
    val initialize : #bot -> unit Lwt.t
    val handle_privmsg : #bot -> string -> string -> unit Lwt.t
end;;

let table : (string, (module Plugin)) Hashtbl.t = Hashtbl.create 7

weather.ml

open Plugins
open Lwt
open Xml

let weather location =
        (* ... *)

module Weather : Plugin = struct
    let initialize bot = return ()
    let handle_privmsg bot chan msg =
        weather msg |> bot#writef "NOTICE %s :%s" chan
end

let () = Hashtbl.replace Plugins.table "weather" (module Weather)