Ruby Enumerator-based lazy flatten method

Question

Michael Harrison has a great post on lazy enumerators in Ruby, providing an implementation of lazy_select and lazy_map. I am wondering whether the following implementation of lazy_flatten should have special processing for anything other than Enumerator and Enumerable types.

class Enumerator

  def lazy_flatten
    Enumerator.new do |yielder|
      self.each do |value|
        if value.kind_of? Enumerator
          value.lazy_flatten.each do |v|
            yielder.yield v
          end
        elsif value.kind_of? Enumerable
          value.flatten.each do |v|
            yielder.yield v
          end
        else
          yielder.yield value
        end
      end
    end
  end

end

Answer 1

1. This doesn't seem lazy to me, as you are still performing old (non-lazy) flatten beneath.
2. Enumerator is Enumerable, so I think you don't need to handle it separately.
3. I would expect lazy_flatten to be method on Enumerable.

Here's how I would implement it:

module Enumerable
  def lazy_flatten
    Enumerator.new do |yielder|
      each do |element|
        if element.is_a? Enumerable
          element.lazy_flatten.each do |e|
            yielder.yield(e)
          end
        else
          yielder.yield(element)
        end
      end
    end
  end
end