Answer-Type Modification without Tears: Prompt-Passing Style Translation for Typed Delimited-Control Operators

The salient feature of delimited-control operators is their ability to modify answer types during computation. The feature, answer-type modification (ATM for short), allows one to express various interesting programs such as typed printf compactly and nicely, while it makes it difficult to embed these operators in standard functional languages. In this paper, we present a typed translation of delimited-control operators shift and reset with ATM into a familiar language with multi-prompt shift and reset without ATM, which lets us use ATM in standard languages without modifying the type system. Our translation generalizes Kiselyov's direct-style implementation of typed printf, which uses two prompts to emulate the modification of answer types, and passes them during computation. We prove that our translation preserves typing. As the naive prompt-passing style translation generates and passes many prompts even for pure terms, we show an optimized translation that generate prompts only when needed, which is also type-preserving. Finally, we give an implementation in the tagless-final style which respects typing by construction.Comment: In Proceedings WoC 2015, arXiv:1606.0583

A continuation semantics of interrogatives that accounts for Baker's ambiguity

Wh-phrases in English can appear both raised and in-situ. However, only in-situ wh-phrases can take semantic scope beyond the immediately enclosing clause. I present a denotational semantics of interrogatives that naturally accounts for these two properties. It neither invokes movement or economy, nor posits lexical ambiguity between raised and in-situ occurrences of the same wh-phrase. My analysis is based on the concept of continuations. It uses a novel type system for higher-order continuations to handle wide-scope wh-phrases while remaining strictly compositional. This treatment sheds light on the combinatorics of interrogatives as well as other kinds of so-called A'-movement.Comment: 20 pages; typo fixe

Lazy Stream Programming in Prolog

In recent years, stream processing has become a prominent approach for incrementally handling large amounts of data, with special support and libraries in many programming languages. Unfortunately, support in Prolog has so far been lacking and most existing approaches are ad-hoc. To remedy this situation, we present lazy stream generators as a unified Prolog interface for stateful computations on both finite and infinite sequences of data that are produced incrementally through I/O and/or algorithmically. We expose stream generators to the application programmer in two ways: 1) through an abstract sequence manipulation API, convenient for defining custom generators, and 2) as idiomatic lazy lists, compatible with many existing list predicates. We define an algebra of stream generator operations that extends Prolog via an embedded language interpreter, provides a compact notation for composing generators and supports moving between the two isomorphic representations. As a special instance, we introduce answer stream generators that encapsulate the work of coroutining first-class logic engines and support interoperation between forward recursive AND-streams and backtracking-generated OR-streams. Keywords: lazy stream generators, lazy lists, first-class logic engines, stream combinators, AND-stream / OR-stream interoperation, Prolog extensionsComment: In Proceedings ICLP 2019, arXiv:1909.0764

Continuations for Comparatives

I extend Barker and Shan\u27s (2014) project of finding natural language applications for continuations to another domain in which it is useful, namely comparatives. I introduce existing analyses of comparatives, in particular Heim 2000, 2006, and Schwarzschild and Wilkinson 2002 and then demonstrate how these analyses can be implemented in the continuations framework

An Operational Foundation for Delimited Continuations

We derive an abstract machine that corresponds to a definitional interpreter for the control operators shift and reset. Based on this abstract machine, we construct a syntactic theory of delimited continuations. Both the derivation and the construction scale to the family of control operators shift_n and reset_n. The definitional interpreter for shift_n and reset_n has n + 1 layers of continuations, the corresponding abstract machine has n + 1 layers of control stacks, and the corresponding syntactic theory has n + 1 layers of evaluation contexts.See also BRICS-RS-05-24