Compiling mix-in modules in OCaml

Learning
1

Hi there, I’m trying to compile a language using mix-in modules (Skel) into OCaml. So basically, let’s say I have some mix-in modules described as such:

module A = struct
  type t
  val x:t
  val y:t
end

module A1 = clone A with type t = int
module A2 = clone A with type t = int, let x = 1
module A3 = clone A with type t = int, let x = 1, let y = 2

A way to translate mix-in modules would be to use abstract types, but then I cannot refine them, so I can’t mimic the clone directive. Another way, would be to use functors, but then it means that A2 is a functor too, which takes as argument a value for y ? This seems fine, until we have a module that clones a lot of other modules, and then it’s less obvious.

Has anybody worked on something similar ? Any input would be greatly appreciated.

2

Can you normalize all mixing constructs away by partial evaluation at translation time?

3

This is not an issue for me anymore, we chose another system.

But for the sake of the discussion, I found few works related to the subject. It seems Tom Hirschowitz and Xavier Leroy worked some time ago on designing a module system for OCaml based on mixins (1, 2), but since Xavier Leroy’s proposal for recursive modules (3) dates back to this period, I suppose they figured it was sufficient to do the part (to which I’m not sure I entirely agree, I take issue with the raise Undefined_recursive_module, but it’s not up to me :upside_down_face:).

I believe normalizing away all mixin constructs is a valid solution, but I don’t find it very satisfactory, since it doesn’t allow to keep the translation close to the source. I have not found an option I prefer though, but as I said, it’s not in my research focus anymore. Thanks for the input :slight_smile: