Module Type_with_layout

module Type_with_layout: sig .. end
S-expressions annotated with relative source positions and comments

module Make: 
functor (Pos : sig
type t 
val sexp_of_t : t -> Type.t
end) -> sig .. end
module Parsed: Make(Src_pos.Absolute).S 
parsing produces absolute positions
include Make(Src_pos.Relative).S
val relativize : Parsed.t_or_comment -> t_or_comment