How can I make a ruby enumerator that does lazy iteration through two other enumerators?

This seems to work just how I want;

enums.lazy.flat_map{|enum| enum.lazy }

Here's the demonstration. Define these yielding methods with side-effects;

def test_enum
  return enum_for __method__ unless block_given?
  puts 'hi'
  yield 1
  puts 'hi again'
  yield 2
end  

def test_enum2
  return enum_for __method__ unless block_given?
  puts :a
  yield :a
  puts :b
  yield :b
end  

concated_enum = [test_enum, test_enum2].lazy.flat_map{|en| en.lazy }

Then call next on the result, showing that the side effects happen lazily;

[5] pry(main)> concated_enum.next
hi
=> 1
[6] pry(main)> concated_enum.next
hi again
=> 2