A look back on OCaml since 2011(ocamlpro.com)

    module LtInt = struct
      type t = int
      (* Use built-in polymorphic comparison *)
      let compare = compare
    end

    module GtInt = struct
      type t = int
      let compare lhs rhs = compare rhs lhs
    end

    module LtIntSet = Set.Make(LtInt)

    module GtIntSet = Set.Make(GtInt)

    module type Monoid = sig
      type t
      val op : t -> t -> t
      val e : t
    end

    module Addition = struct
      type t = int
      let op = (+)
      let e = 0
    end

    module Multiplication = struct
      type t = int
      let op = ( * )
      let e = 1
    end

    module FoldLeft (M : Monoid) = struct
      let fold_left = List.fold_left M.op M.e
    end