Abstract. The subject of this paper is functional program transformation in the so-called point-free style. By this we mean first translating programs to a form consisting only of categorically-inspired combinators, algebraic data types defined as fixed points of functors, and implicit recursion through the use of type-parameterized recursion patterns. This form is appropriate for reasoning about programs equationally, but difficult to actually use in practice for programming. In this paper we present a collection of libraries and tools developed at Minho with the aim of supporting the automatic conversion of programs to point-free (embedded in Haskell), their manipulation and rule-driven simplification, and the (limited) automatic application of fusion for program transformation. 1

Program understanding tools manipulate program representations, such as abstract syntax trees, controlflow graphs, or data-flow graphs. This paper deals with the use of visitor combinators to conduct such manipulations. Visitor combinators are an extension of the well-known visitor design pattern. They are small, reusable classes that carry out specific visiting steps. They can be composed in different constellations to build more complex visitors. We evaluate the expressiveness, reusability, ease of development, and applicability of visitor combinators to the construction of program understanding tools. To that end, we conduct a case study in the use of visitor combinators for control-flow analysis and visualization as used in a commercial Cobol program understanding tool.

Abstract. Binary relational algebra provides semantic foundations for major areas of computing, such as database design, state-based specification, and functional programming. Remarkably, static checking support in these areas fails to exploit the full semantic content of relations. In particular, properties such as the simplicity or injectivity of relations are not statically enforced in operations that manipulate relations, such as database queries, state transitions, or composition of functional components. We describe how a pointfree treatment of relations, their properties, their operators, and the laws that govern them can be captured in a type-directed strategic rewriting system for transformation of relational expressions. This rewriting tool can be used to simplify relational proof obligations and ultimately reduce them to tautologies. We demonstrate how such reductions provide extended static checking (ESC) for design contraints commonly found in software modeling and development.

The dominant share of software development costs is spent on software maintenance, particularly the process of updating programs in response to changing requirements. Currently, such program changes tend to be performed using text editors, an unreliable method that often causes many errors. In addition to syntax and type errors, logical errors can be easily introduced since text editors cannot guarantee that changes are performed consistently over the whole program. All these errors can cause a correct and perfectly running program to become instantly unusable. It is not surprising that this situation exists because the “text-editor method” reveals a low-level view of programs that fails to reflect the structure of programs. We address this problem by pursuing a programming-language-based approach to program updates. To this end we discuss in this paper the design and requirements of an update language for expressing update programs. We identify as the essential part of any update language a scope update that performs coordinated update of the definition and all uses of a symbol. As the underlying basis for update languages, we define an update calculus for updating lambda calculus programs. We develop a type system for the update calculus that infers the possible type changes that can be caused by an update program. We demonstrate that type-safe update programs that fulfill certain structural constraints preserve the type correctness of lambda terms. The update calculus can serve as a basis for higher-level update languages, such as for Haskell or Java.

CWI is a founding member of ERCIM, the European Research Consortium for Informatics and Mathematics. CWI's research has a theme-oriented structure and is grouped into four clusters. Listed below are the names of the clusters and in parentheses their acronyms.

Abstract Exercises in mathematics are often solved using a standard procedure, such as for example solving a system of linear equations by subtracting equations from top to bottom, and then substituting variables from bottom to top. Students have to practice such procedural skills: they have to learn how to apply a particular strategy to an exercise. E-learning systems offer excellent possibilities for practicing procedural skills. The first explanations and motivation for a procedure that solves a particular kind of problems are probably best taught in a class room, or studied in a book, but the subsequent practice can often be done behind a computer. There exist many e-learning systems or intelligent tutoring systems that support practicing procedural skills. The tools vary widely in breadth, depth, user-interface, etc, but, unfortunately, almost all of them lack sophisticated techniques for providing immediate feedback. If feedback mechanisms are present, they are hard coded in the tools, often even with the exercises. This situation hampers the usage of e-learning systems for practicing mathematical skills. This paper introduces a formalism for specifying strategies for solving exercises. It shows how a strategy can be viewed as a language in which sentences consist of transformation steps. Furthermore, it discusses how we can use advanced techniques from computer science, such as term rewriting, strategies, error-correcting parsers, and parser combinators to provide feedback at each intermediate step from the start towards the solution of an exercise. Our goal is to obtain e-learning systems that give immediate and useful feedback. 1

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Traversal strategies provide an established means of describing automated queries, analyses, transformations, and other non-trivial computations on deeply structured data (including, most notably, data representations of software artifacts such as programs). The resulting traversal programs are prone to programming errors. We are specifically concerned with errors that go beyond classic type errors, in particular: (i) divergence of traversal, (ii) unintentional extent of traversal into data, (iii) trivial traversal results, (iv) inapplicability of the constituents of a traversal program along traversal. We deliver a taxonomy of programming errors, and start attacking some of them by refinements of traversal programming.

Embedded systems can be viewed as scaled-down versions of their stand-alone counterparts. In many cases, the software abstractions and libraries for embedded systems can be derived from libraries for stand-alone systems. One such example is the Java library for Java Virtual Machines. An embedded system does not always support all features as in the case of an embedded JVM that does not support floating-point operations. In such cases, an existing library needs to be migrated to the embedded platform. Libraries are large collections of code and manual migration is a daunting task. In this paper, we provide an automated approach to the library migration problem using program transformations. The solution developed in this paper enables rapid adaptation and re-targeting of Java libraries in the presence of evolving libraries and evolving embedded platforms.

This document presents an annotated bibliography of Stratego and closely related projects. The document is organized into sections each dealing with aspects such as language design, implementation and applications