Dynamic rebinding for marshalling and update, with destruct-time ?

Abstract

Most programming languages adopt static binding, but for distributed programming an exclusive reliance on static binding is too restrictive: dynamic binding is required in various guises, for example when a marshalled value is received from the network, containing identifiers that must be rebound to local resources. Typically it is provided only by ad-hoc mechanisms that lack clean semantics.In this paper we adopt a foundational approach, developing core dynamic rebinding mechanisms as extensions to simply-typed callby-value λ-calculus. To do so we must first explore refinements of the call-by-value reduction strategy that delay instantiation, to ensure computations make use of the most recent versions of rebound definitions. We introduce redex-time and destruct-time strategies. The latter forms the basis for a λmarsh calculus that supports dynamic rebinding of marshalled values, while remaining as far as possible statically-typed. We sketch an extension of λmarsh with concurrency and communication, giving examples showing how wrappers for encapsulating untrusted code can be expressed. Finally, we show that a high-level semantics for dynamic updating can also be based on the destruct-time strategy, defining a λupdate calculus with simple primitives to provide type-safe updating of running code. We thereby establish primitives and a common semantic foundation for a variety of real-world dynamic rebinding requirements.

Dynamic rebinding for marshalling and update, via redex-time and destruct-time reduction

“…The proofs for the redex-time and destructtime calculi are slightly different to those for the usual λ c calculus, but they are essentially routine. Detailed proofs can be found in the technical report (Bierman et al 2003b).…”

“…Theorem 4 of the paper (Bierman et al 2003a) asserted the observational equivalence of the three calculi λ c , λ r and λ d , as a check that the latter two are essentially CBV despite their rather different evaluation strategies. After publication, we discovered a technical flaw in the original proof, and so in the technical report (Bierman et al 2003b) we stated and proved the property for a simpler language, replacing letrec by a non-terminating Ω (with Ω −→ Ω).…”

“…Proofs of results are given in the Appendices. This paper is a revised and extended version of the paper (Bierman et al 2003a), with differences as follows: in §3 the typing and run-time error rules are included, and additional examples given; in §4, the error rules for λ marsh are included and the extension with distributed communication is fleshed out with examples, typing and semantics; §7 extends the basic updating calculus to more full-featured Erlang-style (Armstrong et al 1996) dynamic update (Bierman et al 2003c); finally, §8 relates the work herein to our subsequent work on distributed programming and dynamic updating in full-scale programming languages.…”

“…After publication, we discovered a technical flaw in the original proof, and so in the technical report (Bierman et al 2003b) we stated and proved the property for a simpler language, replacing letrec by a non-terminating Ω (with Ω −→ Ω). A proof of the original result has now been completed, using an intricate operational correspondence argument.…”

“…We summarise the main points here; the full details appear in Stoyle's PhD thesis (Stoyle 2006). The proofs of the other technical results are straightforward; we give outlines here and refer the reader to the technical report (Bierman et al 2003b) for details.…”