a b s t r a c tStratego/XT is a language and toolset for program transformation. The Stratego language provides rewrite rules for expressing basic transformations, programmable rewriting strategies for controlling the application of rules, concrete syntax for expressing the patterns of rules in the syntax of the object language, and dynamic rewrite rules for expressing context-sensitive transformations, thus supporting the development of transformation components at a high level of abstraction. The XT toolset offers a collection of flexible, reusable transformation components, and tools for generating such components from declarative specifications. Complete program transformation systems are composed from these components. This paper gives an overview of Stratego/XT 0.17, including a description of the Stratego language and XT transformation tools; a discussion of the implementation techniques and software engineering process; and a description of applications built with Stratego/XT.

The Asf+Sdf Meta-environment is an interactive development environment for the automatic generation of interactive systems for constructing language definitions and generating tools for them. Over the years, this system has been used in a variety of academic and commercial projects ranging from formal program manipulation to conversion of COBOL systems. Since the existing implementation of the Meta-environment started exhibiting more and more characteristics of a legacy system, we decided to build a completely new, component-based, version. We demonstrate this new system and stress its open architecture.

We describe a language for defining term rewriting strategies, and its application to the production of program optimizers. Valid transformations on program terms can be described by a set of rewrite rules; rewriting strategies are used to describe when and how the various rules should be applied in order to obtain the desired optimization effects. Separating rules from strategies in this fashion makes it easier to reason about the behaviof of the optimizer as a whole, compared to traditional monolithic optimizer implementations. We illustrate the expressiveness of our language by using it to describe a simple optimizer for an ML-like intermediate representation.The basic strategy language uses operators such as sequential composition, choice, and recursion to build transformers from a set of labeled unconditional rewrite rules. We also define an extended language in which the sideconditions and contextual rules that arise in realistic optimizer specifications can themselves be expressed as strategydriven rewrites. We show that the features of the basic and extended languages can be expressed by breaking down the rewrite rules into their primitive building blocks, namely matching and building terms in variable binding environments. This gives us a low-level core language which has a clear semantics, can be implemented straightforwardly and can itself be optimized. The current implementation generates C code from a strategy specification.

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C e n t r u m v o o r W i s k u n d e e n I n f o r m a t i c a Software ENgineeringDisambiguation filters for scannerless generalized LR parsers