I'm trying to play with the new private type abbreviations in OCaml
3.11+beta1

If I write:

module type S =
sig
  type t = private int
  val create : int -> t
end;;

module M : S =
struct
  type t = int
  let create x = x
end;;

let x = M.create 0;;

Shouldn't I now be able to say:

string_of_int x;;

But I get a type error... I'm struggling to see what difference the private
declaration has made, therefore.

I thought that the point of private types was that you could deconstruct
them... so values of type M.t are valid wherever an int is used but not the
converse.

Or have I missed something? <prepares to be embarrassed...>


David