Abstract Tabling is probably the most widely studied extension of Prolog. But despite its importance and practicality, tabling is not implemented by most Prolog systems. Existing approaches require substantial changes to the Prolog engine, which is an investment out of reach of most systems. To enable more widespread adoption, we present a new implementation of tabling in under 600 lines of Prolog code. Our lightweight approach relies on delimited control and provides reasonable performance.

Object-oriented programming languages are losing pace with the rapidly evolving Web Services paradigm. They are unable to deal with the distributed, volatile nature of web services, and they lack expressive language constructs for complex web service interactions. In this paper, we present ServiceJ, a Java extension with integrated support for web service programming. By extending the type system with type qualifiers, ServiceJ realizes important objectives from both paradigms. On one hand, ServiceJ resembles Java by promoting reuse and abstraction, and by supporting type- safe web service invocations. On the other hand, ServiceJ supports late web service binding, Quality of Service negotiation, and transparent web service failover. We provide an in-depth discussion of our type system extension, formally prove its type soundness, and compare our language extension with related object-oriented and service-oriented programming languages.

Ever since their invention 30 years ago, checked exceptions have been a point of much discussion. On the one hand, they increase the robustness of software by preventing the manifestation of unanticipated checked exceptions at run-time. On the other hand, they decrease the adaptability of software because they must be propagated explicitly, and must often be handled even if they cannot be signalled.We show that the problems with checked exceptions are caused by a lack of expressiveness of the exceptional return type of a method, which currently dictates a copy & paste style. We add the required expressiveness by introducing anchored exception declarations, which allow the exceptional behavior of a method to be declared relative to that of others. We present the formal semantics of anchored exception declarations, along with the necessary rules for ensuring compile-time safety, and give a proof of soundness. We show that anchored exception declarations do not violate the principle of information hiding when used properly, and provide a guideline for when to use them.We have implemented anchored exception declarations in Cappuccino, which is an extension to the ClassicJava programming language.