Today’s Erlang Thursday is calendar:valid_date/3.

Originally, I was thinking it was going to be calendar:time_difference/3, but then I looked into the Erlang documentation for the calendar module. and saw that it was marked as obsolete, so today I present calendar:valid_date/3.

The arguments to calendar:valid_date/3 are an integer for the year, integer for the month, and an integer for the day. calendar:valid_date/3 returns the atom true if the day passed in is a valid date, and the atom false if it is not a valid date.

calendar:valid_date(2015, 04, 31).
% false
calendar:valid_date(2015, 04, 30).
% true
calendar:valid_date(2015, 02, 29).
% false
calendar:valid_date(2012, 02, 29).
% true
calendar:valid_date(2015, 11, 31).
% false
calendar:valid_date(2015, 11, 76).
% false
calendar:valid_date(2015, 17, 13).
% false

Just a quick check for our sanity that the day this post was published is a valid date as well.

calendar:valid_date(2015, 04, 23).
% true

Now let’s try to break this a bit and test to see how it can handle 0‘s and negative integer values.

calendar:valid_date(-1, 04, 23).
% false
calendar:valid_date(2015, -7, 21).
% false
calendar:valid_date(2015, 7, -13).
% false
calendar:valid_date(0, 0, 0).
% false

As one might hope, unless you deal with B.C. era dates often, a date with a negative value is not a valid date.

Erlang also provides a calendar:valid_date/1 that takes a tuple of the year, month, and day values as well.

calendar:valid_date({2015, 11, 76}).
% false
calendar:valid_date({2015, 04, 23}).
% true

–Proctor