Asynchronous control flow patterns with streams
Going through the examples that we have presented so far, it should be clear that streams can be useful not only to handle I/O, but also as an elegant programming pattern that can be used to process any kind of data. But the advantages do not end at its simple appearance; streams can also be leveraged to turn "asynchronous control flow" into "flow control," as we will see in this section.
Sequential execution
By default, streams will handle data in sequence. For example, the _transform() function of a Transform stream will never be invoked with the next chunk of data until the previous invocation completes by calling callback(). This is an important property of streams, crucial for processing each chunk in the right order, but it can also be exploited to turn streams into an elegant alternative to the traditional control flow patterns.
Some code is always better than too much explanation, so let's...
