Rewriting and call-time choice


Non-confluent and non-terminating rewrite systems are interesting from the point of view of programming. In particular, existing functional logic languages use such kind of rewrite systems to define possibly non-strict non-deterministic functions. The semantics adopted for non-determinism is call-time choice, whose combination with non-strictness is not a trivial issue that has been addressed from a semantic point of view in the Constructor-based Rewriting Logic (CRWL) framework. In a recent serie of works we have investigated how to express call-time choice and non-strict semantics from a point of view closer to classical rewriting. We propose a notion of rewriting which uses an explicit representation for sharing with let-constructions and is proved to be equivalent to the CRWL approach. During this talk we will address the following issues: We will briefly review some of the main existing approaches for describing the semantics of functional logic languages: CRWL, traditional rewriting and Curry’s à la Launchbury operational semantics. We will present the let-rewriting relation for first order functional logic programs, and its semantic equivalence with CRWL logic. We will discuss the relation between all these semantic approaches, and present some technicall results concerning this relations. We will see some interesting properties of the combined framework CRWL/letrewriting, and show by a case study (correctness of bubbling) the usefulness of the achieved combination of semantic and reduction notions. We will extend our let-rewriting relation providing a notion of let-narrowing which is adequate for call-time choice as proved by soundness and completeness results of let-narrowing with respect to let-rewriting. Completeness is based on a lifting lemma for let-rewriting similar to Hullot’s lifting lemma for ordinary rewriting and narrowing.

Cite this paper

@inproceedings{Rodrguez2009RewritingAC, title={Rewriting and call-time choice}, author={Juan Rodr{\'i}guez}, year={2009} }