PHP is one of the most popular languages for server-side application development. The language is highly dynamic, providing programmers with a large amount of flexibility. However, these dynamic features also have a cost, making it difficult to apply traditional static analysis techniques used in standard code analysis and transformation tools. As part of our work on creating analysis tools for PHP, we have conducted a study over a significant corpus of open-source PHP systems, looking at the sizes of actual PHP programs, which features of PHP are actually used, how often dynamic features appear, and how distributed these features are across the files that make up a PHP website. We have also looked at whether uses of these dynamic features are truly dynamic or are, in some cases, statically understandable, allowing us to identify specific patterns of use which can then be taken into account to build more precise tools. We believe this work will be of interest to creators of analysis tools for PHP, and that the methodology we present can be leveraged for other dynamic languages with similar features.

All software evolves, and programming languages and programming language tools are no exception. And just like in ordinary software construction, modular implementations can help ease the process of changing a language implementation and its dependent tools. However, the syntactic and semantic dependencies between language features make this a challenging problem. In this paper we detail how programming languages can be implemented in a modular fashion using the Rascal meta-programming language.Rascal supports extensible definition of concrete syntax, abstract syntax and operations on concrete and abstract syntax trees like matching, traversal and transformation. As a result, new language features can be added without having to change existing code. As a case study, we detail our solution of the LDTA'11 Tool Challenge: a modular implementation of Oberon-0, a relatively simple imperative programming language. The approach we sketch can be applied equally well to the implementation of domain-specific languages.

This short paper introduces M3, a simple and extensible model for capturing facts about source code for future analysis. M3 is a core part of the standard library of the Rascal meta programming language. We motivate it, position it to related work and detail the key design aspects.

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Abstract. We compare the Visitor pattern with the Interpreter pattern, investigating a single case in point for the Java language. We have produced and compared two versions of an interpreter for a programming language. The first version makes use of the Visitor pattern. The second version was obtained by using an automated refactoring to transform uses of the Visitor pattern to uses of the Interpreter pattern. We compare these two nearly equivalent versions on their maintenance characteristics and execution efficiency. Using a tailored experimental research method we can highlight differences and the causes thereof. The contributions of this paper are that it isolates the choice between Visitor and Interpreter in a realistic software project and makes the difference experimentally observable.