Purity is a framework for building applications following a Source->Consumer pattern. A Source is an object which emits Events, a Consumer is an object which listens for Events from a single Source. A Consumer may consume a Source directly, or it may consume it by proxy over a Stream<String>. Any infrastructure which supports Stream<String> will support the Purity framework, for example, it will work directly in memory, or over a HTTP connection.
Learning to use Purity is best done by following examples: