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Rephrasing of dynamic module selection problem
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Date: 2006-02-21 (00:54)
From: Nathan Cooprider <coop@c...>
Subject: Rephrasing of dynamic module selection problem
So I am still trying to get modules to be dynamically (run-time) 
selectable instead of only statically (compile-time). The closest I have 
come to so far is bellow. I want to be able to choose between a set of 
modules (hello1 and hello2 in this example) fairly transparently.

[coop@ender example]$ cat hello1.ml
type t = int
let of_int i =
let print i =
  print_int i;
  print_string " says Hello1\n"

[coop@ender example]$ cat hello2.ml
type t = float
let of_int i =
  float_of_int i
let print i =
  print_float i;
  print_string " says Hello2\n"

[coop@ender example]$ cat main.ml
module Hello1 = struct
  #include "hello1.ml"
end ;;
module Hello2 = struct
  #include "hello2.ml"
end ;;
(* This works . . . *)
module H = Hello1
(* But I would like this to be something like this instead:
let parameter = 1
module H =
  match parameter with
    1 -> Hello1
  | _ -> Hello2

let argument = 42
let main () =
  H.print (H.of_int argument) ;;
main ();;

[coop@ender example]$ cpp main.ml > foo.ml ; ocamlc foo.ml ; rm foo.ml ; 
42 says Hello1

In my real application, there are five different modules (and I am 
adding more after I get this working) and they have around fifty 
functions in them.