Abstract: A computer programming system provides animated program sources that are created in an interactive visual manner. Animation is integrated with computer programming to allow a user or programmer to visualize programming flow and operation. Animated depictions are thus produced for dynamic phenomenon, such as concurrent computations. The program system supports a computation model of concurrent communicating agents. A concrete metaphor for the computation model is provided, e.g. agents are implemented as buildings; rules or methods are implemented robots or workers inside of buildings; local state is posted on bulletin boards inside of buildings; couriers carry messages between buildings; and so on.