Object-oriented Programming with Gradual Abstraction

We describe an experimental object-oriented programming lan-guage, ASL2, that supports program development by means of a series of abstraction steps. The language allows immediate object construction, and it is possible to use the constructed objects for concrete problem solving tasks. Classes and class hierarchies can be derived from the objects- via gradual abstraction steps. We in-troduce two levels of object classification, called weak and strong object classification. Strong object classification relies on conven-tional classes, whereas weak object classification is looser, and less restrictive. As a central mechanism, weakly classified objects are allowed to borrow methods from each other. ASL2 supports class generalization, as a counterpart to class specialization and inheri-tance in mainstream object-oriented programming languages. The final abstraction step discussed in this paper is a syntactical abstrac-tion step that derives a source file with a syntactical class form. Categories and Subject Descriptors D.3.3 [Programming Lan-guages]: Classes and objects General Terms Object-oriented programming, objects before classes, weak and strong classification of objects, abstraction steps