Using Oberon's active objects for language interoperability and compilation

The modern run-time environments provide a high-level object-oriented programming model, reflection capabilities, and a large amount of libraries. These platforms are particularly suitable to host programs written in many different languages. To let all languages reuse the common libraries, the platform has a reflection mechanisms to access the metadata information, which can be used by the compilers to provide language interoperability in a seamless way. Writing a compiler for such platforms becomes an exercise in programming model mapping. Most of the languages rely on closely related flavors of the object-oriented model, but the mappings from one model to another are not always trivial. This thesis investigates the implementation of a language interoperability platform based on an active object-based object-oriented model. First, it analyzes the relations between the type systems of the platform and its subset used for interoperability, and the languages for the platform. Each language type system must be mappable to the platform type system, and the interoperability type system must be bidirectionally mappable to every language type system. Many languages implement a different flavor of the object-oriented model. A few simple mapping rules to transform each flavor onto another one are presented. Second, the Aos kernel implementing Active Oberon’s active object model is introduced as language interoperability platform. The language Active Oberon is presented as natural notation for the active object model. The Paco scope-parallel Active Oberon compiler is a case study that shows a non-trivial application relying on active objects. It parses each scope concurrently and solves forward references in the code with parser synchronization, instead of requiring a second parsing pass. Third, the Jaos Java Virtual Machine for Aos is presented. The jit-compiler maps the Java model to the active object model, and compiles the java byte-code using the data-layout and facilities provided by the kernel; the jit-compiler and the Java reflection libraries use the same metadata repository as the Active Oberon compiler: this allows both languages to interoperate seamlessly. Plugins for the metadata repository and for the kernel’s dynamic loader allow to use multiple metadata persistency formats and multiple object-file formats at the same time.