added split in the result of Set.Make

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@6202 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02

stdlib/moreLabels.mli

@@ -115,6 +115,7 @@ module Set : sig
       val min_elt : t -> elt
       val max_elt : t -> elt
       val choose : t -> elt
+      val split: elt -> t -> t * bool * t
     end
   module Make : functor (Ord : OrderedType) -> S with type elt = Ord.t
 end

stdlib/set.ml

@@ -48,6 +48,7 @@ module type S =
     val min_elt: t -> elt
     val max_elt: t -> elt
     val choose: t -> elt
+    val split: elt -> t -> t * bool * t
   end
 
 module Make(Ord: OrderedType) =

stdlib/set.mli

@@ -136,6 +136,14 @@ module type S =
     (** Return one element of the given set, or raise [Not_found] if
        the set is empty. Which element is chosen is unspecified,
        but equal elements will be chosen for equal sets. *)
+
+    val split: elt -> t -> t * bool * t
+    (** Splitting.  [split x s] returns a triple [(l, present, r)] where
+        - [l] is the set of elements of s that are < x
+        - [r] is the set of elements of s that are > x
+        - [present] is false if [s] contains no element equal to [x],
+          or true if [s] contains an element equal to [x]. *)
+
   end
 (** Output signature of the functor {!Set.Make}. *)