López Fraguas, Francisco J.Martín Martín, EnriqueRodríguez Hortalá, JuanSánchez Hernández, Jaime2023-06-192023-06-192014-031471-068410.1017/S1471068412000373https://hdl.handle.net/20.500.14352/35084Non-confluent and non-terminating constructor-based term rewrite systems are useful for the purpose of specification and 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 a non trivial issue, addressed years ago from a semantic point of view with the Constructor-based Rewriting Logic (CRWL), a well-known semantic framework commonly accepted as suitable semantic basis of modern functional logic languages. A drawback of CRWL is that it does not come with a proper notion of one-step reduction, which would be very useful to understand and reason about how computations proceed. In this paper we develop thoroughly the theory for the first order version of letrewriting, a simple reduction notion close to that of classical term rewriting, but extended with a let-binding construction to adequately express the combination of call-time choice with non-strict semantics. Let-rewriting can be seen as a particular textual presentation of term graph rewriting. We investigate the properties of let-rewriting, most remarkably their equivalence with respect to a conservative extension of the CRWL-semantics coping with let-bindings, and we show by some case studies that having two interchangeable formal views (reduction/semantics) of the same language is a powerful reasoning tool. After that, we provide 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 letre writing. Moreover, we relate those let-rewriting and let-narrowing relations (and hence CRWL) with ordinary term rewriting and narrowing, providing in particular soundness and completeness of let-rewriting with respect to term rewriting for a class of programs which are deterministic in a semantic sense.engjournal articlehttp://journals.cambridge.org/action/displayFulltext?type=1&fid=9188677&jid=TLP&volumeId=14&issueId=02&aid=9188675&bodyId=&membershipNumber=&societyETOCSession=open access004.415.2519.768004.432.4Term rewriting systemsconstructor-based rewriting logicnarrowingnondeterminismcall-time choice semanticssharinglocal bindingsLenguajes de programaciónSistemas expertos1203.23 Lenguajes de Programación