REScala: integrate reactive values with advanced event system

Part of the EScala, REScala, JEScala systems, a paper on REScala:

Traditionally, object-oriented software adopts the Observer pattern to implement reactive behavior. Its drawbacks are well-documented and two families of alternative approaches have been proposed, extending object-oriented languages with concepts from functional reactive and dataflow programming, respectively event-driven programming. The former hardly escape the functional setting; the latter do not achieve the declarativeness of more functional approaches. In this paper, we present RESCALA, a reactive language which integrates concepts from event-based and functional-reactive programming into the object-oriented world. RESCALA supports the development of reactive applications by fostering a functional declarative style which complements the advantages of object- oriented design.

There's example code available from the projects' web page.