Zonnon is a member of the Pascal family of languages, which has two beneficial consequences: a) it is a general purpose language and b) it is immediately familiar to Pascal, Modula-2 and Oberon programmers. Most Pascal programs from the domain of algorithms and data structures are successfully compiled by the Zonnon compiler after just a few minor modifications. However, from the perspective of “programming-in-the-large”, Zonnon is much more elaborate compared to its predecessors. There are four different kinds of program units in Zonnon: objects, modules, definitions and implementations. The first two are instantiated at runtime, the third is a compile time unit of abstraction, and the fourth is a unit of composition. Here is a brief characterization:
Object is a self-contained run-time program component. It can be instantiated dynamically under program control in arbitrary multiplicity.
Module can be considered as a singleton object whose creation is controlled by the system. In addition, a module may act as a container of logically connected abstract data types, operators, and structural units of the runtime environment. In combination with the import relation, the module construct is a powerful system structuring tool.
Definition is an abstract view on an object from a certain perspective. It is a facet of the object or, in other words, an abstract presentation of one or more of its services.
Implementation typically provides a possibly partial default implementation of the corresponding definition. It is a unit of reuse and composition that is aggregated into the state space of an object, either at compile time or at runtime.
Compositional model
Zonnon uses a compositional inheritance model based on aggregation. Typically, an object is composed of a number of functional components, each of them presenting itself to clients in the form of an abstract definition. The set of definitions plus the object’s intrinsic interface constitutes the interface between the object and its clients.
Concurrency model
Zonnon allows adding behavior to objects. For this purpose, the notion of active object was imported from the Active Oberon language and generalized towards a unified model of hierarchic activities. Activities are encapsulated threads that come in two flavors: local activities and agent activities.
Local activities
Local activities express intrinsic object dynamics. A typical context is a block of statements representing the “launch logic” for a set of mutually independent activities, with the assumption that the end of the block acts as a barrier that cannot be passed before all activities have terminated.
Agent activities
Agent activities control the interoperability of objects in terms of formal dialogs. Each agent activity within a “callee” object serves as a template of a formal dialog between some caller and the callee. Agent activities typically implement a parser for some predefined syntax that constitutes a kind of contract between the two communication partners. Formal dialogs are a generalization of asynchronous method calls. This is reflected in the form of a syntax that is borrowed from ordinary method calls.
