Maude as a Metalanguage 1

One of the key goals of rewriting logic from its beginning has been to provide a semantic and logical framework in which many models of computation and languages can be naturally represented. There is by now very extensive evidence supporting the claim that rewriting logic is indeed a very exible and simple logical and semantic framework. From a language design point of view the obvious question to ask is: how can a rewriting logic language best support logical and semantic framework applications, so that it becomes a metalanguage in which a very wide variety of logics and languages can be both semantically deened, and implemented? Our answer is: by being reeective. This paper discusses our latest language design and implementation work on Maude as a reeective metalanguage in which entire environments|including syntax deenition, parsing, pretty printing, execution, and input/output|can be deened for a language or logic L of choice.