let monday_of_week week year =
  let r = call_array ~fn:"Date::Calc::Monday_of_Week"
            [sv_of_int week; sv_of_int year] in
  match r with
      [year; month; day] -> int_of_sv year, int_of_sv month, int_of_sv day
    | _ -> failwith "Pl_Date_Calc: monday_of_week: unexpected return value"