LFE Friday - calendar:day_of_the_week/3
Today’s LFE Friday covers calendar:day_of_the_week/3.
calendar:day_of_the_week/3 allows you to get the day of the week a day occurred on when passed a year, a month and a day.
The first argument represents the year and must be a non-negative integer. The second argument is the month and must be an integer value between 1 and 12 inclusive, representing the 12 months of the Gregorian Calendar, with January being month one. The final argument to
calendar:day_of_the_week/3 is the date, and is expected to be a integer between 1 and 31 inclusive.
calendar:day_of_the_week/3 returns an integer value in between 1 and 7 inclusive, with a return value of 1 representing Monday, and a 7 being Sunday.
> (calendar:day_of_the_week 1 1 1) 1 > (calendar:day_of_the_week 1970 1 1) 4 > (calendar:day_of_the_week 1999 12 31) 5 > (calendar:day_of_the_week 0 1 1) 6
As you can see that the publish date of this LFE Friday post1, 2015-04-10, returns a 5, which is in fact a Friday according to Erlang.
> (calendar:day_of_the_week 2015 4 10) 5
There is also a
calendar:day_of_the_week/1 function which has all the same constraints but instead of taking three arguments, takes one argument that is a three-tuple of the year, month, and day.
> (calendar:day_of_the_week #(2015 4 10)) 5 > (calendar:day_of_the_week #(1970 1 1)) 4 > (calendar:day_of_the_week #(1999 12 31)) 5
And in the spirit of helping to recognize error messages when we see them, let’s take a look at what we get when we pass some invalid inputs to
> (calendar:day_of_the_week 0 0 0) exception error: function_clause in (: calendar date_to_gregorian_days 0 0 0) in calendar:day_of_the_week/3 (calendar.erl, line 151) > (calendar:day_of_the_week 1970 2 31) exception error: if_clause in calendar:date_to_gregorian_days/3 (calendar.erl, line 116) in calendar:day_of_the_week/3 (calendar.erl, line 151) > (calendar:day_of_the_week 1970 13 2) exception error: function_clause in (: calendar last_day_of_the_month1 1970 13) in calendar:date_to_gregorian_days/3 (calendar.erl, line 115) in calendar:day_of_the_week/3 (calendar.erl, line 151)
If you look at the error messages you see that
calendar:date_to_gregorian_days/3, which we will cover in next week’s LFE Friday.
At least the day which should be the publish day. ↩