Identifiable (docs.findlib-1.base.Base.Identifiable)

module type Arg = sig ... end

module type Arg_with_comparator = sig ... end

module type S = sig ... end

module Make (M : Arg) : S with type t := M.t

Used for making an Identifiable module. Here's an example.

module Make_using_comparator
  (M : Arg_with_comparator) : 
  S with type t := M.t with type comparator_witness := M.comparator_witness