The Beauty of Perl 6 Parameter Passing (4 tags)
Perl 6 isn't quite out yet, but you can learn and play with it today in various incarnations. One of the most compelling new features is a revamped and revised mechanism of parameter passing. Phil Crow demonstrates how powerful it is, and how you can gradually adopt more and more powerful constructs.
Using Bloom Filters (3 tags)
Perl hashes make set membership easy at the cost of memory usage. A lesser-known technique, Bloom filters, trades a tunable false-positive rate for compactness -- and has interesting applications for privacy concerns. Maciej Ceglowski explains the theory and practice of Bloom filters.
Math and XSLT (2 tags)
XSLT is primarily for transforming text, but you can use it to do basic math too.