I have a question related to private type abbreviations

I'm interfacing C++ and ocaml and I want to make sure that the ranges of integer types are correct and reflect them in the ocaml interface.

So I define

type uint8 = private int

and

type int8 = private int

same for the other sizes/signedness

and the appropriate functions to do range checking (those are external and use

std::numeric limits)

external uint8 : int -> uint8 = "make_uint8"

...

this gives typesafety and avoids boxing/unboxing and makes sure that the user can

only pass values that are range checked at the earliest opportunity.

Now I wanna check my code

for all the types I wanna use 1 checking function something like this:

let test_conversions (the_fun : int -> 't) (the_val : int) =

try

let the_t = the_fun the_val in

Printf.printf "Numbers are %d\n" (the_t : 't :> int)

with

| Invalid_argument str -> Printf.printf "Error: %s" str

let () = test_conversions uint8 1 -> will work

let () = test_conversions uint64 (-1) -> will print Error...

Now this doesn't typecheck because the type var 't in the signature is too general.

what I need to put there is "a type coercible to int"

Is that possible? Is there some way to achieve this?

Thanks in advance,

Immanuel