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Unfold/fold Transformations Preserving Termination Properties

Summary: Unfold/fold Transformations Preserving
Termination Properties
Torben Amtoft
Computer Science Department, Aarhus University
Ny Munkegade, DK-8000 °Arhus C, Denmark
Abstract. The unfold/fold framework constitutes the spine of many pro-
gram transformation strategies. However, by unrestricted use of folding the
target program may terminate less often than the source program. Several
authors have investigated the problem of setting up conditions of syntactic
nature, i.e. not based on some well-founded ordering of the arguments, which
guarantee preservation of termination properties. These conditions are typ-
ically formulated in a way which makes it hard to grasp the basic intuition
why they work, and in a way which makes it hard to give elegant proofs of
correctness. The aim of this paper will be to give a more unified treatment
by setting up a model which enables us to reason about termination preser-
vation in a cleaner and more algebraic fashion. The model resembles a logic
language and is parametrized with respect to evaluation order, but it should
not be too difficult to transfer the ideas to other languages.
1 Introduction
The unfold/fold framework for program transformation dates back to (at least)


Source: Amtoft, Torben - Department of Computing and Information Sciences, Kansas State University


Collections: Computer Technologies and Information Sciences