Compiling Prolog to Idiomatic Java

Today, Prolog is often used to solve well-defined, domain-specific problems that are part of larger applications. In such cases, a tight integration of the Prolog program and the rest of the application, which is commonly written in a different language, is necessary. One common approach is to compile the Prolog code to (native) code in the target language. In this case, the effort necessary to build, test and deploy the final application is reduced. However, most of the approaches that achieve reasonable performance compile Prolog to object-oriented code that relies on some kind of virtual machine (VM). These VMs are libraries implemented in the target language and implement Prolog's execution semantics. This adds a significant layer to the object-oriented program and results in code that does not look and feel native to developers of object-oriented programs. Further, if Prolog's execution semantics is implemented as a library the potential of modern runtime environments for object-oriented programs, such as the Java Virtual Machine, to effectively optimize the program is more limited. In this paper, we report on our approach to compile Prolog to high-level, idiomatic object-oriented Java code. The generated Java code closely resembles code written by Java developers and is effectively optimized by the Java Virtual Machine.