Re: [Caml-list] writing a very basic plugin system

[Pat Johnson <johnson@crans.org>]

Le 17/01/2012 01:04, Martin DeMello a écrit :
> What is the best mechanism to write the following basic plugin system?
> Plugins should provide two functions, `usage ()` and `handle :
> [string] ->  unit`, and the main interpreter will receive args of the
> form `plugin-name [arg1; arg2; ...]. The problem with the main handle
> function below is that it's twice as long as necessary - I should be
> able to capture the pattern "if there are 0 args call usage else call
> handle" more succinctly. Ideally, I just want to have a mapping of
> plugin name to plugin and have the rest of the code handled
> generically.

This can easily be dealt with 3.12 capabilities :

module type Plugin =
  sig
  val usage : unit -> unit
  val handle : string list -> unit
end;;

(* let's assume A and B are declared accordingly *)

let handle m args =
let module Plug = val
  begin
   match m with
    "a" -> A
    "b" -> B
| _-> raise Not_found
  end : Plugin
in match args with
[] -> Plug.usage ()
| xs -> Plug.handle xs;;

Hope this helps,

-- 
PJ