gistfile1.rb

# Ruby-2.0.0-preview1

module ProjectEuler
  refine Enumerator::Lazy do

    def method_missing(method, *args, &block)
      if method.to_s =~ /multiple_of_(.*)$/
        multiple_of $1.to_i, args[0].to_i
      else
        super
      end
    end

    def multiple_of(multiple, number)
      number % multiple == 0
    end

    def select_multiples_of_3_and_5
      select { |x| multiple_of_3(x) || multiple_of_5(x) }
    end

    def then_sum
      reduce(:+)
    end
  end
end

class WithoutEuler
  def self.call_multiple_of_3_on_lazy
    (1..5).lazy.select_multiples_of_3_and_5
  end
end

class FunctionalRuby
  using ProjectEuler

  def self.sum_multiples_of_3_and_5_for_range(range)
    range.lazy.select_multiples_of_3_and_5.then_sum
  end

end

describe "Ruby 2.0 features" do
  context "Multiples of 3 and 5" do
    it "Sum of all the multiples of 3 or 5 below 1000" do
      FunctionalRuby.sum_multiples_of_3_and_5_for_range((1..1000)).should eq(234168)
    end
  end
end