No abstract

No abstract

Abstract. Tag elimination is a program transformation for removing unnecessary tagging and untagging operations from automatically generated programs. Tag elimination was recently proposed as having immediate applications in implementations of domain specific languages (where it can give a two-fold speedup), and may provide a solution to the long standing problem of Jones-optimal specialization in the typed setting. This paper explains in more detail the role of tag elimination in the implementation of domain-specific languages, presents a number of significant simplifications and a high-level, higher-order, typed self-applicable interpreter. We show how tag elimination achieves Jones-optimality.

Abstract. The phrase optimal program specialization" was de nedby Jones et al. in 1993 to capture the idea of a specializer being strong enough to remove e n tire layers of interpretation. As it has become clear that it does not imply optimality" in the everyday meaning of the word, we propose to rename the concept Jones-optimality". We argue that the 1993 de nition of Jones-optimality is in principle impossible to ful l for strongly typed languages due to necessary encodings on the inputs and outputs of a well-typed self-interpreter. We propose a technical correction of the de nition which allows Jones-optimality t o remain a meaningful concept for typed languages. We extend recent w ork by Hughes and by T aha and Makholm on the long-unsolved problem of Jones-optimal specialization for strongly typed languages. The methods of Taha and Makholm are enhanced to allow almost optimal" results when a self-interpreter is specialized to a typeincorrect program; how to do this has been an open problem since 1987. Neither Hughes' nor Taha Makholm's methods are by themselves sucient for Jones-optimal specialization when the language contains primitive operations that produce or consume complex data types. A simple postprocess is proposed to solve the problem. An implementation of the proposed techniques has been produced and used for the rst successful practical experiments with truly Jones-optimal specialization for strongly typed languages.

Previous type systems for mobility calculi (the original Mobile Ambients, its variants and descendants, e.g., Boxed Ambients and Safe Ambients, and other related systems) offer little support for generic mobile agents. Previous systems either do not handle communication at all or globally assign fixed communication types to ambient names that do not change as an ambient moves around or interacts with other ambients. This makes it hard to type examples such as a messenger ambient that uses communication primitives to collect a message of non-predetermined type and deliver it to a non-predetermined destination.In contrast, we present our new type system PolyA. Instead of assigning communication types to ambient names, PolyA assigns a type to each process P that gives upper bounds on (1) the possible ambient nesting shapes of any process P to which P can evolve, (2) the values that may be communicated at each location, and (3) the capabilities that can be used at each location. Because PolyA can type generic mobile agents, we believe PolyA is the first type system for a mobility calculus that provides type polymorphism comparable in power to polymorphic type systems for the λ-calculus. PolyA is easily extended to ambient calculus variants. A restriction of PolyA has principal typings.