### code.ml [ocaml]
open Batteries

module type N = sig
  type t
  val make: unit -> t
  val add_to_self: t -> t -> unit
  val as_float: t -> float
end

module Int: N = struct
  type t = int ref
  let make () = ref 1
  let add_to_self x y = x := !x + !y
  let as_float = (!) |- float_of_int
end

module Float: N = struct
  type t = float ref
  let make () = ref 0.5
  let add_to_self x y = x := !x +. !y
  let as_float = (!) |- identity
end

let which_module = function
  | "float" -> (module Float: N)
  | "int" -> (module Int: N)
  | _ -> invalid_arg "which_module"

let parse: string -> (module N with type t = 'a) * 'a = fun (type a) s ->
  let module C = (val (which_module s): N) in
  (module C: N), C.make ()

### error.txt
File "code.ml", line 30, characters 2-72:
Error: This `let module' expression has type (module N) * C.t
In this type, the locally bound module name C escapes its scope
Command exited with code 2.