Software applications must react to external changes such as the input from the user and network messages. Traditionally, object-oriented software adopts the Observer pattern to implement reactivity and decouple the observers from the observables. Whereas researchers have highlighted the drawbacks of this style for a long time, alternatives struggle to be widely accepted. In particular, functional reactive programming and dataflow programming - which aim to represent time-changing values as first class abstractions - are promising, but hardly escape the functional setting. On the other hand, event-based languages directly support events but do not achieve the declarative style of more functional approaches.

REScala is 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 and declarative style which complements the advantages of object-oriented design.