A Semantics of Introspection in a Re ectivePrototype - Based

In Malenfant et al. 19], we have described a reeective model for a prototype-based language based on the lookup apply reeective introspection protocol. In this paper, we augment our previous protocol by converting it to handle continuations reiied as rst-class objects. First-class continuations provide much more control over the current computation; during the introspection phase red by message sending, they make it possible not only to change the behavior of the program for that message but also for the entire future computation. In this paper, we provide this introspection protocol with a formal semantics. This result is obtained by exhibiting a mapping from program conngurations to priority rewrite systems (PRS) as well as a mapping from message expressions to ground rst-order terms used to query the PRS. Other advantages of this approach are: to ensure the termination of the introspection using the smallest set of formally justiied conditions and to provide a clear declarative account of this reeective protocol. The PRS also appears as a meta-level to the base language, independent of the implementation, but from which we derive fundamental clues to obtain an eecient language processor. By our new model, we nally highlight the link between reeection in object-oriented languages and the one originally proposed by 3-Lisp 24], although object-orientation provides reusability to reeection, making it easier to use.