Module Comparator

module Comparator: sig .. end
A type-indexed value that allows one to compare (and for generating error messages, serialize) values of the type in question.

One of the type parameters is a phantom parameter used to distinguish comparators potentially built on different comparison functions. In particular, we want to distinguish those using polymorphic compare and those using a monomorphic compare.


type ('a, 'witness) t = private {
   compare : 'a -> 'a -> int;
   sexp_of_t : 'a -> Sexplib.Sexp.t;
}
type ('a, 'b) comparator = ('a, 'b) t 
module type S = sig .. end
module type S1 = sig .. end
module Poly: S1  with type 'a t = 'a
module S_to_S1: 
functor (S : S) -> S1 with type 'a t = S.t with type comparator_witness = S.comparator_witness

The Make functors mint fresh types that are used as the phantom comparator_witnesses.
module Make: 
functor (M : sig
type t 
val sexp_of_t : t -> Sexplib.Sexp.t
val compare : t -> t -> int
end) -> S with type t := M.t
module Make1: 
functor (M : sig
type 'a t 
val compare : 'a t -> 'a t -> int
val sexp_of_t : 'a t -> Sexplib.Sexp.t
end) -> S1 with type 'a t := 'a M.t