JFP 18 (4): 437–502, 2008. c 2007 Cambridge University Press 437 doi:10.1017/S0956796807006600 First published online 17 October 2007 Printed in the United Kingdom Dynamic rebinding for marshalling and update, via redex-time and destruct-time reduction PETER SEWELL University of Cambridge (e-mail:
[email protected]) GARETH STOYLE University of Cambridge (e-mail:
[email protected]) MICHAEL HICKS University of Maryland, College Park (e-mail:
[email protected]) GAVIN BIERMAN Microsoft Research, Cambridge (e-mail:
[email protected]) KEITH WANSBROUGH Data Connection Ltd., Edinburgh (e-mail:
[email protected]) 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 the simply typed call-by- 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.