Hello,

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