OT: Recurring Event library?

["Josh Rehman" <java.josh@verizon.net>]

This is certainly off topic, but I don't really know where else to turn.

Is there an open source library, perhaps in Perl or Java, that supports
the representation and manipulation of date recurrence patterns? We are
looking to describe patterns like "every Thursday" or "every Tue-Thurs"
or even "on the first Monday of February". Ideally such a library would
provide us with a variety of views, including natural language. Anyone
who has used a PIM knows the thing I am speaking of (Evolution, Outlook,
etc).

The brute force approach for this problem is straight-forward and would
not require a third party library. However, we are looking for an
efficient implementation that can tell us, for example, whether or not a
given date satisfies a given pattern. (The brute force approach expands
the pattern and checks each element for equality with a given date: good
for patterns that describe small sets, bad for ones that describe larger
sets).

Thanks for helping,
Josh Rehman