The Synthesis of Implementations for Abstract Data Types

Abstract

Program transformation offers a systematic way of developing correct and efficient programs from specifications. The formal system, outlined in Burstall and Darlington [1977], that has become known as the unfold/fold system, offers a very simple formal base which is nevertheless capable of achieving a wide class of transformations. However significant transformations expressed solely in terms of these rules became too complex to be communicated or achieved by a system. To overcome these problems we are developing a transformation meta-language that allows transformations to be explicated in a structured way without removing the formal base of these transformations. Constructs in this meta-language consist of higher level transformation processes or tactics such as combine loops, remove recursion or re-use storage. These are ultimately expressible in terms of the unfold/fold steps but provide a richer vocabulary for communicating transformation plans either to man or machine. One of the more useful of these tactics is one that enables implementations for abstract data types to be synthesised automatically. In this paper we consider this transformation process in some detail and use it to exemplify our ideas on structuring program transformations and the sort of systems that we envisage being developed.