Calculate the date number for a specified week of a year, the two input parameters are the year and a week number, output is the date number of the SUNDAY of the week. The predicate day_of_week/2 also works with date numbers.
This predicate is located in the file 'datetime.txt', use ensure_loaded/1 to include this file.
see also: age/7 day_number/4 day_of_week/2 datetime module decode_date/4 decode_datetime/7 decode_time/4 encode_date/4 encode_datetime/7 encode_time/2 encode_time/3 encode_time/4 ensure_loaded/1 first_week/2 leap_year/1 length_month/3 monday_of_week/3 monday_of_week/5 next_week/4 num_weeks_in_year/2 reverse_day_number/4
| Example | |
| start_of_week(1998, 1, DateNum). | succeeds, DateNum = 729386 |
| start_of_week(1998, 2, DateNum), decode_date(DateNum, Year, Month, Day). | Succeeds and the calculated date of the sunday of week 2 of
1998 is 4 January 1998 DateNum = 729393 Year = 1998 Month = 1 Day = 4 |
| start_of_week(1999, 20, DateNum), decode_date(DateNum, Year, Month, Day). | Succeeds and the calculated date of the sunday of week 20 of
1999 is 16 May 1999 DateNum = 729890 Year = 1999 Month = 5 Day = 16 |
| Exceptions | |
| The Year and/or WeekNumber parameters are not integers | a type_error(evaluable, Value) exception is thrown, Value is unified with the incorrect argument |
| The DateNumber parameter is an integer nor a variable | a type_error(evaluable, Value) exception is thrown, Value is unified with the incorrect argument |