Scala fuses object-oriented and functional programming in a statically typed programming language. It is aimed at the construction of components and component systems. This paper gives an overview of the Scala language for readers who are familar with programming methods and programming language design.

We identify three programming language abstractions for the construction of reusable components: abstract type members, explicit selftypes, and modular mixin composition. Together, these abstractions enable us to transform an arbitrary assembly of static program parts with hard references between them into a system of reusable components. The transformation maintains the structure of the original system. We demonstrate this approach in two case studies, a subject/observer framework and a compiler front-end.

www.iam.unibe.ch/∼scg Unanticipated changes to complex software systems can introduce anomalies such as duplicated code, suboptimal inheritance relationships and a proliferation of run-time downcasts. Refactoring to eliminate these anomalies may not be an option, at least in certain stages of software evolution. Classboxes are modules that restrict the visibility of changes to selected clients only, thereby offering more freedom in the way unanticipated changes may be implemented, and thus reducing the need for convoluted design anomalies. In this paper we demonstrate how classboxes can be implemented in statically-typed languages like Java. We also present an extended case study of Swing, a Java GUI package built on top of AWT, and we document the ensuing anomalies that Swing introduces. We show how Classbox/J, a prototype implementation of classboxes for Java, is used to provide a cleaner implementation of Swing using local refinement rather than subclassing.

One of the problems facing developers is the constant evolution of components that are used to build applications. This evolution is typical of any multi-person or multi-site software project. How can we program in this environment? More precisely, how can language design address such evolution? In this paper we attack two significant issues that arise from constant component evolution: we propose language-level extensions that permit multiple, co-existing versions of classes and the ability to dynamically upgrade from one version of a class to another, whilst still maintaining type safety guarantees and requiring only lightweight extensions to the runtime infrastructure. We show how our extensions, whilst intuitive, provide a great deal of power by giving a number of examples. Given the subtlety of the problem, we formalize a core fragment of our language and prove a number of important safety properties.

Scala fuses object-oriented and functional programming in a statically typed programming language. It is aimed at the construction of components and component systems. This paper gives an overview of the Scala language for readers who are familar with programming methods and programming language design.

This paper describes how the Erlang programming language could be extended with parameterized modules, in a way that is compatible with existing code. This provides a powerful way of creating callbacks, that avoids the limitations involved with function closures, and extends current programming practices in a systematic way that also eliminates a common source of errors. The usage of parameterized modules is similar to Object-Oriented programming, and is naturally complemented by the currently underused feature of behaviours (interface declarations), which are also explained in detail.

Software must be adapted to accommodate new features in the context of changing requirements. In this paper, we illustrate how applications with aspect weaving capabilities can be easily and dynamically adapted with unforseen features. Aspects were used at three levels: in the context of semantic analysers, within a BPEL engine that orchestrates Web Services, and finally within BPEL processes themselves. Each level uses its own tailored domain-specific aspect language that is easier to manipulate than a generalpurpose one (close to the programming language) and the pointcuts are independent from the implementation.

In this paper we address some of the the issues in versioning for a Java like language. In particular we address the issues of using multiple versions of a library at the same time. We present a series of solutions that statically, and link-time, ensure the absents of type errors.