Communicating Functional Agents and Their Application to Graphical User Interfaces

We demonstrate how concepts of communicating agents can be integrated into purely functional languages by an orthogonal extension of the usual I/O monad. These agents communicate via so-called service access points and support programming in the style of client-server architectures. We then show the feasibility of the approach by applying it to the example of graphical user interfaces, which we consider to be a typical instance of reactive systems. For this purpose we develop the concept of so-called gates, which serve as a mediator between user events and the application logic. It turns out that the combination of functional expressiveness and concurrency yields a powerful framework for the realization of reactive systems such as graphical user interfaces. All concepts discussed in this paper are represented in the functional language Opal and have been implemented in the Opal programming environment.