LFE Friday - calendar:valid_date/3

This week's LFE Friday was translated with permission from the Erlang Thursday series by Steven Proctor. This week's translator: Robert Virding.

Today's LFE Friday 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 24)
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 24)  
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 24))
true

-Proctor, Robert