Abstract not found

Dynamic binding and delimited control are useful together in many settings, including Web applications, database cursors, and mobile code. We examine this pair of language features to show that the semantics of their interaction is ill-defined yet not expressive enough for these uses. We solve this open and subtle problem. We formalise a typed language DB+DC that combines a calculus DB of dynamic binding and a calculus DC of delimited control. We argue from theoretical and practical points of view that its semantics should be based on delimited dynamic binding: capturing a delimited continuation closes over part of the dynamic environment, rather than all or none of it; reinstating the captured continuation supplements the dynamic environment, rather than replacing or inheriting it. We introduce a type- and reduction-preserving translation from DB + DC to DC, which proves that delimited control macro-expresses dynamic binding. We use this translation to implement DB + DC in Scheme, OCaml, and Haskell. We extend DB + DC with mutable dynamic variables and a facility to obtain not only the latest binding of a dynamic variable but also older bindings. This facility provides for stack inspection and (more generally) folding over the execution context as an inductive data structure.

Starting from a continuation-based interpreter for a simple logic programming language, propositional Prolog with cut, we derive the corresponding logic engine in the form of an abstract machine. The derivation originates in previous work (our article at PPDP 2003) where it was applied to the lambda-calculus. The key transformation here is Reynolds's defunctionalization that transforms a tail-recursive, continuation-passing interpreter into a transition system, i.e., an abstract machine. Similar denotational and operational semantics were studied by de Bruin and de Vink (their article at TAPSOFT 1989), and we compare their study with our derivation. Additionally, we present a direct-style interpreter of propositional Prolog expressed with control operators for delimited continuations.

Abstract. A CPS translation is a syntactic translation of programs, which is useful for describing their operational behavior. By iterating the standard call-by-value CPS translation, Danvy and Filinski discovered the CPS hierarchy and proposed a family of control operators, shift and reset, that make it possible to capture successive delimited continuations in a CPS hierarchy. Although shift and reset have found their applications in several areas such as partial evaluation, most studies in the literature have been devoted to the base level of the hierarchy, namely, to level-1 shift and reset. In this article, we investigate the whole family of shift and reset. We give a simple calculus with level-n shift and level-n reset for an arbitrary n> 0. We then give a set of equational axioms for them, and prove that these axioms are sound and complete with respect to the CPS translation. The resulting set of axioms is concise and a natural extension of those for level-1 shift and reset.

Abstract. We propose type systems that abstractly interpret small-step rather than big-step operational semantics. We treat an expression or evaluation context as a structure in a linear logic with hypothetical reasoning. Evaluation order is not only regulated by familiar focusing rules in the operational semantics, but also expressed by structural rules in the type system, so the types track control flow more closely. Binding and evaluation contexts are related, but the latter are linear. We use these ideas to build a type system for delimited continuations. It lets control operators change the answer type or act beyond the nearest dynamically-enclosing delimiter, yet needs no extra fields in judgments and arrow types to record answer types. The typing derivation of a directstyle program desugars it into continuation-passing style. 1

Abstract—Polarized logic is the logic of values and continuations, and their interaction through continuation-passing style. The main limitations of this logic are the limitations of CPS: that continuations cannot be composed, and that programs are fully sequentialized. Delimited control operators were invented in response to the limitations of classical continuation-passing. That suggests the question: what is the logic of delimited continuations? We offer a simple account of delimited control, through a natural generalization of the classical notion of polarity. This amounts to breaking the perfect symmetry between positive and negative polarity in the following way: answer types are positive. Despite this asymmetry, we retain all of the classical polarized connectives, and can explain “intuitionistic polarity ” (e.g., in systems like CBPV) as a restriction on the use of connectives, i.e., as a logical fragment. Our analysis complements and generalizes existing accounts of delimited control operators, while giving us a rich logical language through which to understand the interaction of control with monadic effects. I.

We study the control operators ”control” and ”prompt” which manage part of continuations, that is, delimited continuations. They are similar to the well-known control operators ”shift” and ”reset”, but differ in that the former is dynamic, while the latter is static. In this paper, we introduce a static type system for ”control ” and ”prompt” which does not use recursive types. We design our type system based on the dynamic CPS transformation recently proposed by Biernacki, Danvy and Millikin. We also introduce let-polymorphism into our type system, and show that our type system satisfies several important properties such as strong type soundness.