An Algebraic Theory of Actors and Its Application to a Simple Object-Based Language

The development of Simula by Ole-Johan Dahl and Kristen Nygaard introduced a number of important programming language concepts – object which supports modularity in programming through encapsulation of data and procedures, the concept of class which organizes behavior and supports Abstract Data Types, and the concept inheritance which provides subtyping relations and reuse [6]. Peter Wegner terms programming languages which use objects as object-based languages, and reserves the term object-oriented languages for languages which also support classes and inheritance [58].