A graphical tool for observing state and behavioral changes at join points

To comprehend programs or to fix a bug, programmers always mentally simulate the program execution by reading the source code. Aspect-oriented programming (AOP) increases this mental effort, because it can alter the state and the behavior of the base program at a join point to any extent by executing advices. Advices are implicitly invoked in the source code and their compositions at a join point may vary according to the runtime context. They can access and even change the context values of join points. Without appropriate tools, it is difficult to notice the effects of the implicitly executed advices. The goal of my work is to increase the comprehensibility of AO programs by using a graphical tool, that can succinctly visualize the state and behavioral changes at join points

A Pointcut Language for Setting Advanced Breakpoints

In interactive debugging, it is an essential task to set breakpoints specifying where a program should be suspended at runtime to allow interaction. A debugging session may use multiple logically related breakpoints so that the sequence of their (de)activations leads to the expected suspension with the least irrelevant suspensions. A (de)activation is sometimes decided by some runtime context values related to that breakpoint. However, existing breakpoints, which are mainly based on line locations, are not expressive enough to describe the logic and the collaboration. Programmers have to manually perform some repeated tasks, thus debugging efficiency is decreased. In this paper, we identify five frequently encountered debugging scenarios that require to use multiple breakpoints. For such scenarios, it is often easier than using the traditional debugger to write pointcuts in an aspect-oriented language, and to suspend the execution at the selected join points. However, existing languages cannot handle the scenarios neatly and uniformly. Therefore, we design and implement a breakpoint language that uses pointcuts to select suspension times in the program. Our language allows programmers to use comprehensible source-level abstractions to define breakpoints. Also, multiple breakpoints can be freely composed to express their collaboration. In this way, an expected suspension can be expressively programmed and reached with less or even no irrelevant suspensions

A Pure Embedding of Roles: Exploring 4-dimensional Dispatch for Roles in Structured Contexts

Present-day software systems have to fulfill an increasing number of requirements, which makes them more and more complex. Many systems need to anticipate changing contexts or need to adapt to changing business rules or requirements. The challenge of 21th-century software development will be to cope with these aspects. We believe that the role concept offers a simple way to adapt an object-oriented program to its changing context. In a role-based application, an object plays multiple roles during its lifetime. If the contexts are represented as first-class entities, they provide dynamic views to the object-oriented program, and if a context changes, the dynamic views can be switched easily, and the software system adapts automatically. However, the concepts of roles and dynamic contexts have been discussed for a long time in many areas of computer science. So far, their employment in an existing object-oriented language requires a specific runtime environment. Also, classical object-oriented languages and their runtime systems are not able to cope with essential role-specific features, such as true delegation or dynamic binding of roles. In addition to that, contexts and views seem to be important in software development. The traditional code-oriented approach to software engineering becomes less and less satisfactory. The support for multiple views of a software system scales much better to the needs of todays systems. However, it relies on programming languages to provide roles for the construction of views. As a solution, this thesis presents an implementation pattern for role-playing objects that does not require a specific runtime system, the SCala ROles Language (SCROLL). Via this library approach, roles are embedded in a statically typed base language as dynamically evolving objects. The approach is pure in the sense that there is no need for an additional compiler or tooling. The implementation pattern is demonstrated on the basis of the Scala language. As technical support from Scala, the pattern requires dynamic mixins, compiler-translated function calls, and implicit conversions. The details how roles are implemented are hidden in a Scala library and therefore transparent to SCROLL programmers. The SCROLL library supports roles embedded in structured contexts. Additionally, a four-dimensional, context-aware dispatch at runtime is presented. It overcomes the subtle ambiguities introduced with the rich semantics of role-playing objects. SCROLL is written in Scala, which blends a modern object-oriented with a functional programming language. The size of the library is below 1400 lines of code so that it can be considered to have minimalistic design and to be easy to maintain. Our approach solves several practical problems arising in the area of dynamical extensibility and adaptation

An In-Depth Look at ALIA4J

New programming languages supporting advanced modularization mechanisms are often implemented as transformations to the imperative intermediate representation of an already established language. But while their core constructs largely overlap in semantics, re-using the corresponding transformations requires re-using their syntax as well; this is limiting. In the ALIA4J approach, we identified dispatching as fundamental to most modularization mechanisms and provide a meta-model of dispatching as a rich, extensible intermediate language. Based on this meta-model, one can modularly implement the semantics of dispatching-related constructs. From said constructs a single execution model can then be derived which facilitates interpretation, bytecode generation, and even optimized machine-code generation. We show the suitability of our approach by mapping five popular languages to this meta-model and find that most of their constructs are shared across multiple languages. We furthermore present implementations of the three different execution strategies together with a generic visual debugger available to any ALIA4J-based language implementation. Intertwined with this paper is a tutorial-style running example that illustrates our approach