. This note introduces Peter Landin's 1965 technical report "A Generalization of Jumps and Labels", which is reprinted in this volume. Its aim is to make that historic paper more accessible to the reader and to help reading it in context. To this end, we explain Landin's control operator J in more contemporary terms, and we recall Burge's solution to a technical problem in Landin's original account. Keywords: J-operator, secd-machine, call/cc, goto, history of programming languages 1. Introduction In the mid-1960's, Peter Landin was exploring functional programming extended with control. Initially, Landin had added the control operator J (for jump) to his language of Applicative Expressions in order to explicate the goto statement from Algol 60 [10]. This general control construct, however, was powerful enough to have independent interest quite beyond the application to Algol: Landin wrote a series of technical reports [11, 12, 13] on functional programming with control, the most si...

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...

Our thesis is that programming web applications with continuations is superior to the current page-centric technology. A continuation is a program-level manageable value representing the rest of the computation of the program. "What to do next" is precisely what has to be explicitly encoded in order to program non trivial web interactions. Continuations allow web applications to be written in direct style that is, as a single program that displays forms and reads form submission since continuations automatically capture everything (control point, lexical bindings, etc.) that is needed to resume the computation. Programming is therefore safer, easier and more re-usable. 1

In this paper, we present Famke. It is a library for Clean that enables the creation and management of independent distributed processes (written in Clean) on a network of computers. The main feature of Famke is that values of any type, i.e. data and code, can be communicated between independent processes in a type safe way. Famke uses Clean's dynamic types and its dynamic linker to extend running applications with new code (plug-ins) that, if its type matches the types used in the application, are guaranteed to fit. Clean no longer o#ers any support for concurrent evaluation, but fortunately, we can realize threads, signalling and exception handling by using first class continuations without the need for additional run-time support. We have made an interactive shell on top of Famke with which the user can manipulate processes interactively.

This paper describes the platform's design, implementation, and performance.

Abstract not found

Virtual machines (vms) have enjoyed a resurgence as a way of allowing the same application program to be used across a range of computer systems. This flexibility comes from the abstraction that the vm provides over the native interface of a particular computer. However, this also means that the application is prevented from taking the features of particular physical machines into account in its implementation. This dissertation addresses the question of why, where and how it is useful, possible and practicable to provide an application with access to lower-level interfaces. It argues that many aspects of vm implementation can be devolved safely to untrusted applications and demonstrates this through a prototype which allows control over run-time compilation, object placement within the heap and thread scheduling. The proposed architecture separates these application-specific policy implementations from the application itself. This allows one application to be used with different policies on different systems and also allows nave or premature optimizations to be removed.

This paper describes a way of expressing --expressions (which produce closures) in terms of ffl--expressions (--expressions containing only local and global variable references) and calls to an interactive compiler that compiles ffl--expressions. This point of view is an interesting way of describing the semantics of --expressions and closure generation. It also leads to an efficient closure implementation both in time and space. A closure is uniformly represented as a piece of code instead of a compound object containing a code and environment pointer. This method can also be used to simulate closures in conventional dialects of Lisp. KEY WORDS Closure implementation Compiling Lisp Scheme Published in: Journal of Computer Languages, Vol. 17, No. 4, pp. 251-267, Pergamon Press, 1992. 1 INTRODUCTION In many lexically scoped dialects of Lisp, e.g. Scheme[1-3], T[4,5] and Common Lisp[6], procedures are first class objects. They are defined by --expressions of the form (lambda formal-...

Abstract. There is a correspondence between classical logic and programming language calculi with first-class continuations. With the addition of control delimiters, the continuations become composable and the calculi become more expressive. We present a fine-grained analysis of control delimiters and formalise that their addition corresponds to the addition of a single dynamically-scoped variable modelling the special top-level continuation. From a type perspective, the dynamically-scoped variable requires effect annotations. In the presence of control, the dynamically-scoped variable can be interpreted in a purely functional way by applying a store-passing style. At the type level, the effect annotations are mapped within standard classical logic extended with the dual of implication, namely subtraction. A continuation-passing-style transformation of lambda-calculus with control and subtraction is defined. Combining the translations provides a decomposition of standard CPS transformations for delimited continuations. Incidentally, we also give a direct normalisation proof of the simply-typed lambda-calculus with control and subtraction.

. Just as a traditional continuation represents the rest of a computation from a given point in the computation, a subcontinuation represents the rest of a subcomputation from a given point in the subcomputation. Subcontinuations are more expressive than traditional continuations and have been shown to be useful for controlling tree-structured concurrency, yet they have previously been implemented only on uniprocessors. This article describes a concurrent implementation of one-shot subcontinuations. Like oneshot continuations, one-shot subcontinuations are first-class but may be invoked at most once, a restriction obeyed by nearly all programs that use continuations. The techniques used to implement one-shot subcontinuations may be applied directly to other one-shot continuation mechanisms and may be generalized to support multi-shot continuations as well. A novel feature of the implementation is that continuations are implemented in terms of threads. Because the implementation model ...