Hello QuillMeantTen,

Thanks for drawing attention to the Doomsday algorithm, it looks interesting.

Given that your code was written as a learning exercise, I will highlight one aspect that stands out as a problem: the use of subroutine prototypes.

First, Perl prototypes don’t function as a programmer coming from C or Java might expect them to, and they’re mostly unneeded anyway. This is explained at length in Tom Christiansen’s article “Far More Than Everything You’ve Ever Wanted to Know about Prototypes in Perl,” which is reprinted as a PerlMonks tutorial here.

But, second, none of the subroutine prototypes in your code is ever actually used — because the & sigil prepended to a subroutine call disables them! See perlsub#Prototypes. Unless you have a good reason to disable prototypes, you should call a subroutine like this:

frobnicate();
[download]

and not like this:

&frobnicate;
[download]

The latter form is seen mainly in legacy code dating from Perl’s earlier days.

Update: Fixed typo.

Hope that helps,