module type ID = sig
    type t
    val of_string : string -> t
    val to_string : t -> string
  end

module StrId : ID =
  struct
    type t = string
    let of_string x = x
    let to_string x = x
  end

module TypeId = StrId
module ServiceId = StrId

(*
utop # TypeId.of_string "abc";;
- : ServiceId.t = <abstr>
 *)

module type ID = sig
    type t
    val of_string : string -> t
    val to_string : t -> string
  end

module StrId : ID =
  struct
    type t = string
    let of_string x = x
    let to_string x = x
  end

module TypeId : ID = StrId
module ServiceId : ID = StrId

(*
utop # TypeId.of_string "abc";;
- : TypeId.t = <abstr>
*)