We present an overview of the program transformation methodology, focusing our attention on the so-called `rules + strategies' approach in the case of functional and logic programs. The paper is intended to offer an introduction to the subject. The various techniques we present are illustrated via simple examples. A preliminary version of this report has been published in: Moller, B., Partsch, H., and Schuman, S. (eds.): Formal Program Development. Lecture Notes in Computer Science 755, Springer Verlag (1993) 263--304. Also published in: ACM Computing Surveys, Vol 28, No. 2, June 1996. 3 1 Introduction The program transformation approach to the development of programs has first been advocated by [Burstall-Darlington 77], although the basic ideas were already presented in previous papers by the same authors [Darlington 72, Burstall-Darlington 75]. In that approach the task of writing a correct and efficient program is realized in two phases: the first phase consists in writing an in...

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This paper concerns our research on developing a theory and methodology appropriate for systematically building complicated Prolog programs. Programs are constructed procedurally from standard components. We identify skeletons, basic Prolog programs with a well-understood control flow, and techniques, standard Prolog programming practices, as basic components. Applying a technique to a skeleton creates an extension of the skeleton. Complicated programs are built by choosing a skeleton and repeatedly applying techniques. Separate extensions of the same skeleton can be composed into a single program, simplifying the process of program development. We describe our application of skeletons and techniques within the framework of Shapiro's Model Inference System. 1.1 INTRODUCTION

The inductive synthesis of recursive logic programs from incomplete information, such as input/output examples, is a challenging subfield both of ILP (Inductive Logic Programming) and of the synthesis (in general) of logic programs from formal specifications. We first overview past and present achievements, focusing on the techniques that were designed specifically for the inductive synthesis of recursive logic programs, but also discussing a few general ILP techniques that can also induce non-recursive hypotheses. Then we analyse the prospects of these techniques in this task, investigating their applicability to software engineering as well as to knowledge acquisition and discovery.

An equational approach to the synthesis of functional and logic program is taken. In this context, the synthesis task involves nding executable equations such that the given speci cation holds in their standard model. Hence, to synthesize such programs, induction is necessary.We formulate procedures for inductiveproof,aswell as for program synthesis, using the framework of \ordered rewriting". We also propose heuristics for generalizing from a sequence of equational consequences. These heuristics handle cases where the deductive process alone is inadequate for coming up with a program. 1.

We present our work on the representation and correctness of program schemas, in the context of logic program synthesis. Whereas most researchers represent schemas purely syntactically as higher-order expressions, we shall express a schema as an open first-order theory that axiomatises a problem domain, called a specification framework, containing an open program that represents the template of the schema. We will show that using our approach we can define a meaningful notion of correctness for schemas, viz. that correct program schemas can be expressed as parametric specification frameworks containing templates that are steadfast, i.e. programs that are always correct provided their open relations are computed correctly.

We present a general strategy for stepwise, sound and progressive synthesis of logic programs from specifications by examples and properties. We particularize this to schema-guided synthesis, and state a generic synthesis theorem. We justify some design choices for the development of a particular synthesis mechanism that is guided by a Divide-and-Conquer schema, is inductive and deductive, is interactive, and features a non-incremental presentation of examples. Some crucial steps of this mechanism are explained, and illustrated by a sample synthesis. We draw some conclusions on our results so far, state some related work, and outline future research directions.

It can be argued that for (semi-)automated software development, program schemas are indispensable, since they capture not only structured program design principles, but also domain knowledge, both of which are of crucial importance for hierarchical program synthesis. Most researchers represent schemas purely syntactically (as higher-order expressions) . This means that the knowledge captured by a schema is not formalised. We take a semantic approach and show that a schema can be formalised as an open (firstorder) logical theory that contains an open logic program. By using a special kind of correctness for open programs, called steadfastness, we can define and reason about the correctness of schemas. We also show how to use correct schemas to synthesise steadfast programs. 1. Introduction It can be argued that any systematic approach to software development must use some kind of schema-based strategies. In (semi-)automated software development, program schemas become indispensable, s...

Deductive synthesis methods derive programs in an incremental manner, and therefore pose a halting problem -- when can synthesis stop with a correct program? We give a characterisation of this problem and state a halting principle as a solution. Another characteristic of deductive synthesis is that it may derive several correct programs, giving rise to another question -- which correct programs are desirable? We show that the answer is related to the halting problem, via the notion of steadfast, or reusable, programs as desirable programs. Our work also reveals that Clark's idea of the completion of a program is central to deductive synthesis, since it is the basis of our halting principle and our notion of steadfast programs. 1 Introduction Writing a correct program is a major problem in programming. It is theoretically interesting and practically significant. Incorrect programs may have dire consequences, and are unfortunately related to the software crisis in practice. Methods have...

Abstract. A long standing problem in logic programming is how to impose directionality on programs in a safe fashion. The benefits of directionality include freedom from explicit sequential control, the ability to reason about algorithmic properties of programs (such as termination, complexity and deadlock-freedom) and controlling concurrency. By using Girard’s linear logic, we are able to devise a type system that combines types and modes into a unified framework, and enables one to express directionality declaratively. The rich power of the type system allows outputs to be embedded in inputs and vice versa. Type checking guarantees that values have unique producers, but multiple consumers are still possible. From a theoretical point of view, this work provides a “logic programming interpretation ” of (the proofs of) linear logic, adding to the concurrency and functional programming interpretations that are already known. It also brings logic programming into the broader world of typed languages and types-as-propositions paradigm, enriching it with static scoping and higher-order features.