# Pastebin uiURjUBy
(* mods.ml *)

module type FooType = sig
  type t
  type e

  val make : e -> t
  val to_string : t -> string
end
;;

module Foo : FooType
= struct
  type e = int
  type t = SomeThing of (e * e)

  let make i = SomeThing (i, i)

  let to_string (SomeThing (i,j)) =
    Printf.sprintf "(%d,%d)" i j
end