Improving Functional Logic Programs By Difference-Lists

Modern multi-paradigm declarative languages integrate features from functional, logic, and concurrent programming. Since programs in these languages make extensive use of fist-processing functions, we consider of much interest the development of list-processing optimization techniques. In this work, we consider the adaptation of the well-known difference-lists transformation from the logic programming paradigm to our integrated setting. Unfortunately, the use of difference-lists is impractical due to the absence of non-strict equality in lazy (call-by-name) languages. Despite all, we have developed a novel, stepwise transformation which achieves a similar effect over functional logic programs. We also show a simple and practical approach to incorporate the optimization into a real compiler. Finally, we have conducted a number of experiments which show the practicality of our proposal.