note: pull-streams are harmonious, because they combine a yang api (reader) with a yin api (readable). try to have a balanced proportion of 'ers and 'ables in your system. pull-streams do this well because every flowing pipeline has a equal number of yins and yangs. Every stream starts with a yin as it's source, and ends in a yang as it's sink. It may go through any number of transform streams, each is a yang that returns a yin. A duplex stream is yin and yang side by side.