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