On Thu, 18 Mar 2004 15:40:06 +0900, Hal Fulton <hal9000 / hypermetrics.com> wrote:

>So the question becomes: Given a date (typically "today") and a list
>of recurring tasks, how do I determine which ones need to be displayed?

I don't get it.  Are you asking for something along the lines of Perl's date-parser in Date::Manip?
If so, then I think you should have a look at the source(s) of the relevant perl functions / methods in Date::Manip.

See also 

http://search.cpan.org/search?query=date-manip&mode=all
http://dates.rcbowen.com/
http://www.perl.com/pub/a/2003/03/13/datetime.html