module type OrderedType = Stdlib.Set.OrderedType

module type S = sig
  include Stdlib.Set.S
  val exists_opt: (elt -> 'a option) -> t -> 'a option
end

module Make(Elt: OrderedType) = struct
  include Stdlib.Set.Make(Elt)

  let exists_opt (type a) (f: elt -> a option) set =
    let exception Found of a in
    let f' x = Option.iter (fun x -> raise (Found x)) (f x) in
    match iter f' set with
    | exception Found x -> Some x
    | _                 -> None
end