How to get removed something and removed object, when you remove something from object in persistence data structure.

int_option_minimum.sml

local
  fun cleanHeadNone nil = nil
    | cleanHeadNone (NONE :: t) = cleanHeadNone t
    | cleanHeadNone (l as SOME _ :: _) = l
  fun cleanEndNone l = (rev o cleanHeadNone o rev) l
  fun simpleMin nil = raise Fail "Empty"
    | simpleMin [NONE] = raise Fail "End with NONE"
    | simpleMin [SOME x] = (x, nil)
    | simpleMin (NONE :: t) = min t
    | simpleMin (SOME x :: t) =
    let
      val (y, t') = min t
    in
      if x < y then (x, NONE :: t)
      else (y, SOME x :: t')
    end
in
(*
 * int option list -> int * int option list
 * ex) [NONE, SOME 2, SOME 3] -> (2, [NONE, NONE, SOME 3])
 *)
fun min l = cleanEndNone (simpleMin l)
end