[Caml-list] writing a very basic plugin system

[Martin DeMello <martindemello@gmail.com>]

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.

module A = struct
    let usage () = print_endline "usage of A"
      let handle args = print_endline "hello from A"
end

module B = struct
    let usage () = print_endline "usage of A"
      let handle args = print_endline "hello from B"
end

      let handle m args = match (m, args) with
        "a", [] -> A.usage ()
      | "a", xs -> A.handle xs
      | "b", [] -> B.usage ()
      | "b", xs -> B.handle xs
      | _, _    -> print_endline "no such module"

      let _ =
        handle "a" [];
        handle "a" ["1"];
        handle "b" [];
        handle "b" ["args"]