Problem 10 on Project Euler

p10.rb

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

  def sqrt
    Math.sqrt self
  end

  def prime?(preprocessed=(2..self.sqrt.floor))
    limit = self.sqrt.floor
    for test in preprocessed
      return true if limit < test
      return false if self.divisible_by? test
    end
    true
  end

  def primes
    ret = []
    3.step(self, 2) do |test|
      ret << test if test.prime? ret
    end
    ret.unshift 2
    ret
  end
end

module Enumerable

  def sum
    inject(0) {|t, c| t + c}
  end

end

puts 1999999.primes.sum