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Research into systematic program construction has the important aim of elevating coding from the realm of arts and entertainment to science and engineering. In this paper we have built a bridge between the pragmatic syntax-based approach of stepwise enhancement and the very theoretical semantic approach of shape and polytypism. Despite the gulf between the research methodologies behind these two approaches, there is a very close relationship between them. This is pleasing in itself but also allows us to see ways in which both approaches can be generalised.

From the work on shape and polytypism in functional languages we have the generality of arbitrary functions as parameters, polymorphic types and the automatic synthesis of certain higher order functions from algebraic types. From the work on stepwise enhancement in logic programming, we have the generality of nondeterminism, additional arguments, flexible modes and use of accumulators. By combining the advantages of both approaches, we have shown how more code in both functional and logic programming languages can be constructed in a systematic and partially automated way. Initial experiences with prototype tools based on these ideas have been very encouraging.

Lee Naish