Does ruby support recursive enumerators?

Question

I'm writing a method to merge two streams of numbers, and I've two alternative implementations:

def merge1(l1, l2)
    Enumerator.new do |yielder|
        h = case l1.peek <=> l2.peek
                when -1 then l1.next
                when +1 then l2.next
                else l1.next; l2.next
                end
        yielder << h
        yielder << merge1(l1, l2).next
    end.lazy              
end

def merge2(l1, l2)
    Enumerator.new do |yielder|
        loop do
            h = case l1.peek <=> l2.peek
                    when -1 then l1.next
                    when +1 then l2.next
                    else l1.next; l2.next
                    end
            yielder << h
        end
    end.lazy              
end
puts merge2((1..Float::INFINITY).lazy.map {|x| x * 2}, (1..Float::INFINITY).lazy.map {|x| x * 3}).first(10)

But merge1 only prints "2 3" while merge2 produces the correct result.

Answer 1

You need to yield each item that sub-enumerator generate:

def merge1(l1, l2)
    Enumerator.new do |yielder|
        h = case l1.peek <=> l2.peek
                when -1 then l1.next
                when +1 then l2.next
                else l1.next; l2.next
                end
        yielder << h
        merge1(l1, l2).each do |h| # <----
          yielder << h             # <----
        end                        # <----
    end.lazy              
end