2011/1/26 Jeremy Yallop <yallop@gmail.com>

On 26 January 2011 12:58, Julien Signoles <julien.signoles@gmail.com> wrote:
> How to convert the following ocaml 3.12 code into a typable ocaml < 3.12
> code?
> I have a solution using Obj. Is it possible without Obj?

There are safer approaches (than Obj) to a "universal type" described here:

http://ocaml.janestreet.com/?q=node/18

Whether your problem can be solved with such an approach depends on
how flexible your definition of "the same [type]" is. You can
certainly write a function of the same type and behaviour as 'f' that
way, though.

I'm aware of such an universal type. It works fine for the small example of my original post. However I see no way to use it on my real case because it is a bit more complex. Actually it looks like:
=====
(* val f: 'a u -> 'a list u *)
type 'a u = ... (* a phantom type, defined in another file *)
let f (type v) (x:v u) =
let module S =
    F(struct
    type t = v u (* waiting a type t of the form w u for some w *)
      let x = x
      (* an additional list of operations over t *)
      let equal = ( = ) (* ... *)
    end)
in
(S.y : v list u) (* S.y is opaque: no way to destruct it *)
=====
I see no way to inject and project values [x] and/or [S.y] to any universal type since the conversion from [x] to [S.y] is done internally by the functor F.

Thanks for your help,
Julien