anchor.diff:  let snapshot () = Common.snapshot push fstar_options ()
   let rollback depth = Common.rollback pop fstar_options depth
   
  -let set_option k v = Util.smap_add (peek()) k v
  +let set_option k v = Util.smap_add (internal_peek()) k v
   let set_option' (k,v) =  set_option k v
   
   let light_off_files : ref<list<string>> = Util.mk_ref []
  
positive.code: let fstar_options : ref<list<list<optionstate>>> = Util.mk_ref []
  
  let internal_peek () = List.hd (List.hd !fstar_options)
  let peek () = internal_peek()
  let pop  () = // already signal-atomic
      match !fstar_options with
      | []
  
negative.code: let parse_warn_error s = snd (parse_warn_error_set_get) () s
  
  let init () =
     let o = internal_peek () in
     Util.smap_clear o;
     defaults |> List.iter set_option'                          //initialize it with the default values
  
  