private class PipeJoin[E]
	super Iterator[E]
	var source1: Iterator[E]
	var source2: Iterator[E]

	redef fun is_ok
	do
		return source1.is_ok or source2.is_ok
	end

	redef fun item
	do
		if source1.is_ok then return source1.item else return source2.item
	end

	redef fun next
	do
		if source1.is_ok then source1.next else source2.next
	end
end