. The functional programming language Clean has a high level I/O system (version 0.8) in which complex yet efficient interactive programs can be created. In this paper we present its successor (version 1.0), the object I/O system. We consider some of the design considerations that have influenced the design of the new I/O system greatly. Key issues are compositionality, orthogonality, and extensibility. Apart from design, the object I/O system improves on its predecessor by two major contributions: programmers can introduce polymorphic local state at every (collection of) user interface component(s) and programmers can create interactive processes in a flexible way. All interface components can communicate with each other by sharing state but also using powerful message passing primitives in both synchronous, asynchronous, and uni- or bi-directional way. Using the message passing mechanism remote procedure calling can be added easily. The result is an object oriented I/O...

v Acknowledgements vi 1

A framework for programming graphical user interfaces (GUIs), called PIDGETS++, is presented. PIDGETS++ enables arbitrary device-independent PostScript graphics descriptions to be composed and manipulated as structured C++ objects. Not only can graphics descriptions be displayed in windows, additionally, they can be equipped with handlers which are invoked whenever a user event occurs while the mouse pointer's hot spot is over the area colored by the graphics description. Thus, arbitrary GUI objects may be constructed as composite graphics descriptions. Moreover, GUI objects are amenable to arbitrary PostScript transformations such as coloring, rotation, scaling, and clipping while staying fully functional. GUI objects are constructed in a declarative style. At the time of its creation, each GUI object's appearance is constrained to be a function of the states of a set of other objects; this constraint is maintained by the PIDGETS++ system throughout the GUI object's lifetime. From a...