LISP and Symbolic Computation, 9(2/3)153-179
A Semantics of Introspection in a Reflective Prototype-Based LanguageJacques Malenfant, D'epartement d'informatique et recherche op'erationnelle, Universit'e de Montr'eal, C.P. 6128, Succursale A, Montr'eal, Qu'ebec, Canada H3C 3J7
Christophe Dony, LIRMM, Universit'e de Montpellier, 161 rue Ada, 34392 Montpellier Cedex 5, France
Pierre Cointe, Ecole des Mines de Nantes, 4 rue Alfred Kastler, La Chantrerie, 44070 Nantes Cedex 03, France
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Abstract: In Malenfant et al. [19], we have described a
reflective model for a prototype-based language based on the lookup s'
apply reflective introspection protocol. In this paper, we augment our
previous protocol by converting it to handle continuations reified as
first-class objects. First-class continuations provide much more
control over the current computation; during the introspection phase
fired 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 1 from program configurations to priority rewrite
systems (PRS) as well as a mapping from message expressions to ground
first-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 justified conditions and to provide a clear
declarative account of this reflective 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 efficient language processor. By our new model, we finally
highlight the link between reflection in object-oriented languages and
the one originally proposed by 3-Lisp [24], although
object-orientation provides reusability to reflection, making it
easier to use.
Keywords: procedural reflection, object-oriented programming, reflective towers, priority rewrite systems, semantics |
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