_no_unused_value_warning_ `with sexp` in utop

Question

I added require "sexplib.syntax";; and core etc in utop.

If I type

module type Printer = sig 
  type t with sexp
end

in utop, it says

module type Printer = sig type t val t_of_sexp : Sexp.t -> t val sexp_of_t : t -> Sexp.t end

ok, this is no problem.

But if I save the above code into a ml file and use it in utop, it gives error:

Error: Unbound type constructor _no_unused_value_warning_

Why? Is this a bug in utop? How can I report?

Answer 1

It is also representable on my system, with

Core 111.11.01
Utop 1.12

It is a bug, for sure. You should report it to Jérémie Dimino, as he is responsible for both core and utop.