Global abstraction-safe marshalling with hash types

Abstract

Type abstraction is a key feature of ML-like languages for writing large programs. Marshalling is necessary for writing distributed programs, exchanging values via network byte-streams or persistent stores. In this paper we combine the two, developing compile-time and run-time semantics for marshalling, that guarantee abstraction-safety between separately-built programs.We obtain a namespace for abstract types that is global, i.e. meaningful between programs, by hashing module declarations. We examine the scenarios in which values of abstract types are communicated from one program to another, and ensure, by constructing hashes appropriately, that the dynamic and static notions of type equality mirror each other. We use singleton kinds to express abstraction in the static semantics; abstraction is tracked in the dynamic semantics by coloured brackets. These allow us to prove preservation, erasure, and coincidence results. We argue that our proposal is a good basis for extensions to existing ML-like languages, pragmatically straightforward for language users and for implementors.

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

“…Part of the motivation for this work is to cope with marshalling of values in distributed functional languages, but this paper does not deal with issues of type coherence between separately-compiled run-times. One might combine λ io marsh with the hash types of [LPSW03]. The λ io marsh calculus has communication on channels but not π-calculus-style new channel generation.…”

Type-safe distributed programming for OCaml

“…In the absence of type abstraction this might work well, but here it seems we would need to propagate abstraction boundaries at runtime, perhaps using some form of the coloured brackets introduced by Grossman et. al [18] and further developed in the Acute semantics [22,33]. This would be complex and costly.…”

“…In previous work we have studied several aspects of this problem, developing theoretical calculi that construct globally meaningful runtime type names freshly [31] and based on code hashes [22], calculi of dynamic rebinding [4], and a prototype language, Acute, to explore the design space further [33,34].…”

Generic Pickling and Minimization

“…The pickler throws an exception if it finds a resource. The pickler does not try to rebind resources (as discussed in [9,16]). Rebinding could however be realized with the transformation mechanism introduced next.…”