```ruby
module LightShow

  # Combine animations.
  class Combination

    # Initialize a new combination of animations. Yields the new instance.
    def initialize
      @animations = []
      yield self
    end

    # Add an animation to this combination.
    def <<(animation)
      @animations << animation
    end

    # Iterate over the combined animations, lazily evaluating each frame.
    #
    # If none or only one animation is provided, no combination is performed.
    # Iteration stops if any animation returns a nil frame.
    def each_frame(previous, &block)
      return if @animations.empty?
      if @animations.size == 1
        # Pass-through, no combining needed
        @animations.each_frame(previous, &block)
      else
        # Wrap each animation as a lazily-evaluated enumerator
        enums = @animations.map do |animation|
          Enumerator.new do |yielder|
            animation.each_frame(previous) do |frame|
              yielder << frame
            end
          end.lazy # lazy is critical!
        end

        # Then zip them together, combining each set of frames
        enums.first.zip(*enums[1..-1]).each do |frames|
          break if frames.any?(&:nil?)
          block.call combine_frames(frames)
        end
      end
    end

    # Combine a set of frames. Override this to define your own behavior.
    def combine_frames(frames)
      raise NotImplementedError, "must implement combine_frames"
    end
  end
end
```

Use the new enumerable approach for Combination
user
```ruby
module LightShow

  # Combine animations.
  class Combination

    # Initialize a new combination of animations. Yields the new instance.
    def initialize
      @animations = []
      yield self
    end

    # Add an animation to this combination.
    def <<(animation)
      @animations << animation
    end

    # Frames for the combined animations, lazily evaluating each frame.
    #
    # If none or only one animation is provided, no combination is performed.
    # Iteration stops if any animation returns a nil frame.
    def frames(previous)
      return [] if @animations.empty?
      return @animations.first.frames(previous) if @animations.size == 1

      # Lazily zip the next frames of each animation together. Ruby 1.9.3
      # doesn't have lazy enumerators or lazy zip, so do it by hand.
      Enumerator.new do |y|
        enums = @animations.map { |anim| anim.frames(previous).each }

        loop do
          begin
            frames = enums.map(&:next)
            y << combine_frames(frames)
          rescue StopIteration
            break
          end
        end
      end
    end

    # Combine a set of frames.
    #
    # Defaults to calling combine_colors with the colors for each pixel.
    #
    # Override this to define your own behavior.
    def combine_frames(frames)
      frames.first.zip(*frames[1..-1]).map do |pixels|
        combine_pixels pixels
      end
    end

    # Combine pixels by calling combine_values on each of r, g, and b.
    def combine_pixels(pixels)
      pixels.first.zip(*pixels[1..-1]).map do |values|
        combine_values values
      end
    end

    def combine_values(colors)
      raise NotImplementedError, "must implement combine_values"
    end
  end
end
```
assistant