with_fun.ml

module Abstract_value :
sig
  type t
  val create : unit -> t
end =
struct
  type t = unit -> unit

  let create () =
    fun () -> ()
end

type t = {
  mutable abstract_value : Abstract_value.t;
  (* Regular fields *)
  x : int;
}

let make ~x = {
  x;
  abstract_value = Abstract_value.create ();
}

(*
   The proper comparison function for this type,
   which is incompatible with Pervasives.compare.
*)
let compare a b =
  compare (abs a.x) (abs b.x)

let (=) a b =
  compare a b = 0

let (<>) a b =
  compare a b <> 0

let (<) a b =
  compare a b < 0

let (<=) a b =
  compare a b <= 0

let (>) a b =
  compare a b > 0

let (>=) a b =
  compare a b >= 0

(*
   Make sure to run these tests with ocamlc, ocamlopt and any other OCaml
   compiler you're using.
*)
let test_exception () =
  try
    ignore (Pervasives.compare (make ~x:0) (make ~x:0));
    false
  with Invalid_argument "equal: functional value" ->
    true

let () =
    print_endline (if test_exception () then "Passed" else "Failed")

Like this?

  $ ocaml test_mj.ml
Passed
 $ ocamlc test_mj.ml -o testmj.byte && testmj.byte
Passed
 $ ocamlopt test_mj.ml -o testmj.opt && testmj.opt
Passed