FizzBuzz as a Regexp - source for http://pastie.org/158799

fizzbuzz.rb

#! /usr/bin/env ruby1.9
puts 1.upto(100).to_a.join("\n").
  gsub(%r{
    (?# matchers for multiples of 3 -- remainder=0,1,2 respectively)
    (?<z>[0369]+(?:\g<u>\g<d>|\g<d>\g<u>)?|\g<u>\g<d>|\g<d>\g<u>){0}
    (?<u>[147]\g<z>?|[258][0369]*\g<d>){0}
    (?<d>[258]\g<z>?|[147][0369]*\g<u>){0}

    (?# fizz/buzz matchers)
    (?<fizz>\g<z>){0}
    (?<buzz>\d*[05]){0}
    (?<fizzbuzz>\g<z>?0|[0369]*\g<u>5){0}

    (?# we must test for fizzbuzz first)
    (?<!\d)(?:\g<fizzbuzz>|\g<buzz>|\g<fizz>)(?!\d)
  }x) {
    case
    when $4; "Fizz"
    when $5; "Buzz"
    when $6; "FizzBuzz"
    end
  }