The last few years have seen a renewed interest in continuations for expressing advanced control structures in programming languages, and new models such as Abstract Continuations have been proposed to capture these dimensions. This article investigates an alternative formulation, exploiting the latent expressive power of the standard continuation-passing style (CPS) instead of introducing yet other new concepts. We build on a single foundation: abstracting control as a hierarchy of continuations, each one modeling a specific language feature as acting on nested evaluation contexts. We show how iterating the continuation-passing conversion allows us to specify a wide range of control behavior. For example, two conversions yield an abstraction of Prologstyle backtracking. A number of other constructs can likewise be expressed i...

ion of Typed Contexts Olivier Danvy & Andrzej Filinski DIKU -- Computer Science Department, University of Copenhagen Universitetsparken 1, 2100 Copenhagen , Denmark uucp: danvy@diku.dk & andrzej@diku.dk Abstract This report investigates abstracting control with functions. This is achieved by defining continuations as functions abstracting lexically a delimited context [C[ ]] rather than dynamically an unlimited one C[ ], as it is usually the case. Because their co-domain is distinguished from the final domain of Answers, such continuations can be composed, and this contrasts with the simple exceptions of ML and Lisp and the unlimited first-class continuations of Scheme. Making these functional control abstractions first-class o#ers a new area in programming which this paper explores. The key points obtained here are: a denotational semantics for a simple, call-by-value, strongly typed expression language with higher-order functions and first-class continuations; its congruence with a ...

: A partial continuation is a prefix of the computation that remains to be done. We propose in this paper a new operator which precisely controls which prefix is to be abstracted into a partial continuation. This operator is strongly related to the notion of dynamic extent which we denotationally characterize. Some programming examples are commented and we also show how to express previously proposed control operators. A suggested implementation is eventually discussed. Keywords: continuation, partial continuation, dynamic and indefinite extent, escape feature. Continuations were introduced within denotational semantics to express the "rest of the computation" in these cases where some constructs of a language can alter it. Non local exits or jumps (stop, goto), exception handling, failure semantics in Prolog-like languages are usually described with continuations [Stoy 77, Schmidt 86]. The Scheme language [Rees & Clinger 86] offers procedural first-class continuations with indefinit...

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Numerous high-level control operators, with various properties, exist in the literature. To understand or compare them is difficult since their definitions use quite different theoretical frameworks; moreover, to our knowledge, no implementation offers them all. This paper tries to explain control operators by the often simple stack manipulation they perform. We therefore present what we think these operators are, in an executable framework derived from abstract continuations. This library is published in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. For instance, we do not claim our implementation to be faithful nor we attempt to formally derive these implementations from their original definitions. The goal is to give a flavor of what control operators are, from an implementation point of view. Last but worth to say, all errors are mine. Among the many existing control operators, w...

The mobile form of distributed computation, called mobile computation, is investigated from the viewpoints of computational model, programming language and implementation. The emphasis of this thesis compared with the related work is on analyzing existing mobile language systems from a rather implementational point of view. The contribution of this thesis is threefold. (1) We present a computational model in which dynamic transference of code, data and execution state can be represented. Several mobility mechanisms in existing mobile language systems are analyzed in the model. (2) Based on the analysis, a programming language for mobile computation is designed. The distinctive feature of the language is the facility to control the transparency of migration. (3) An implementation of the mobile programming language is presented. The language is implemented as an extension of the Java language. The implementation is so portable that the program runs on any standard Java inte...