[sledge] Add Set.pop_min_elt_exn

Differential Revision: D29441151

fbshipit-source-id: b317d6458

sledge/nonstdlib/NSSet.ml

@@ -75,6 +75,11 @@ struct
   let choose_exn = S.choose
   let pop = S.pop_opt
   let pop_exn = S.pop
+
+  let pop_min_elt_exn s =
+    let min = S.min_elt s in
+    (min, S.remove min s)
+
   let only_elt = S.only_elt
   let classify = S.classify
   let map s ~f = S.map f s

sledge/nonstdlib/NSSet_intf.ml

@@ -88,6 +88,9 @@ module type S = sig
   val pop_exn : t -> elt * t
   (** Find and remove an unspecified element. [O(1)]. *)
 
+  val pop_min_elt_exn : t -> elt * t
+  (** Find and remove the minimum element. [O(1)]. *)
+
   (** {1 Transform} *)
 
   val map : t -> f:(elt -> elt) -> t