Sorted list functor

SortedList.ml

type comparison = LT | EQ | GT

module type ORDERED =
sig
  type t
  val compare : t -> t -> comparison
end

module type SORTEDLIST =
  functor (O : ORDERED) ->
sig
  type t
  val from_list : O.t list -> t
end

module OrderedInt : ORDERED =
struct
  type t = int
  let compare a b =
    if a < b then LT
    else if a = b then EQ
    else GT
end

module SortedList : SORTEDLIST = functor (O : ORDERED) ->
struct
  type t = O.t list
  let from_list : O.t list -> t =
    let cmp' a b = match O.compare a b with
                     | LT -> -1
                     | EQ -> 0
                     | GT -> 1
    in List.sort cmp'
end