Preface

This volume contains the formal proceedings of the 5th International Workshop on Rewriting Techniques for Program Transformations and Evaluation (WPTE 2018), held on 8th of Juli 2018 in Oxford, United Kingdom, and affiliated with FLoC 2018 and FSCD 2018.

Scope of WPTE

Rewriting techniques are of great help for studying correctness of program transformations, translations and evaluation, and the aim of WPTE is to bring together the researchers working on program transformations, evaluation, and operationally-based programming language semantics, using rewriting methods, in order to share the techniques and recent developments and to exchange ideas to encourage further activation of research in this area. Topics in the scope of WPTE include the correctness of program transformations, optimisations and translations; program transformations for proving termination, confluence and other properties; correctness of evaluation strategies; operational semantics of programs, operationally-based program equivalences such as contextual equivalences and bisimulations; cost-models for reasoning about the optimizing power of transformations and the costs of evaluation; program transformations for verification and theorem proving purposes; translation, simulation, equivalence of programs with different formalisms, and evaluation strategies; program transformations for applying rewriting techniques to programs in specific programming languages; program transformations for program inversions and program synthesis; program transformation and evaluation for Haskell and rewriting.

Research Paper Selection

At the workshop six research papers were presented of which five were accepted for the postproceedings. Each submission was reviewed by three or four members of the Program Committee in two to three rounds, one round for workshop presentation and at most two rounds for publication to the postproceedings.

The program also included one invited talk by Jean-Pierre Jouannaud (Polytec, Palaiseau, Grand Paris, France) on a framework for graph rewriting; the abstract of this talk is included in this volume.

Acknowledgments

Many people helped to make WPTE 2018 a success. We thank the members of the program committee for their careful reviewing of all submissions and we thank the participants for their valuable contributions. We express our gratitude to all members of the local organization of FLOC 2018 under direction of Marta Kwiatkowska and the conference chair of FSCD 2018. Finally, we thank the editors of EPTCS for the publication of the post-proceedings.

Program Committee

• Joachim Niehren (Chair), Inria, Lille.
• David Sabel (Co-chair), Goethe University, Frankfurt.
• Noaki Nishida, Nagoya University.
• Joachim Breitner, University of Pennsylvania.
• Giulio Guerrieri, Oxford University.
• Manfred Schmidt-Schauß, Goethe-University, Frankfurt.
• Vivek Nigam, Universidade Federal da Paraiba
• Adam Barwell, University of St Andrews.
• Maribel Fernandez, King's College London.

With greeting to the readers of this WPTE edition.

Joachim Niehren and David Sabel

A Framework for Graph Rewriting

Rewriting with graphs enjoys a long history in computer science, graphs being used to represent not only data structures, but also program structures, and even computational models. Termination and confluence techniques have been elaborated for various generalizations of trees, such as rational trees, directed acyclic graphs, lambda terms and lambda graphs. But the design of tools for rewriting arbitrary graphs has made little progress beyond various categorical definitions dating from the mid seventies and the study of the particular families of graphs listed above. This paper describes the generalization of term rewriting techniques to a general class of multigraphs that we call drags, viz. finite, directed, ordered (multi-)graphs. To this end, we develop a rich algebra of drags which allows us to view graph rewriting in exactly the same way as we view term rewriting.