Solution to problem 1 on Project Euler

p1.rb

class Numeric
  def divisible_by? num
    self % num == 0
  end
end

module Enumerable
  def sum &blk
    blk = proc {|x| x} unless block_given?
    inject(0) {|sum, element| sum + (blk[element] || 0)}
  end
end

puts (1...1000).sum {|n| n if n.divisible_by? 3 or n.divisible_by? 5}