4,927 research outputs found
Lazy Evaluation and Delimited Control
The call-by-need lambda calculus provides an equational framework for
reasoning syntactically about lazy evaluation. This paper examines its
operational characteristics. By a series of reasoning steps, we systematically
unpack the standard-order reduction relation of the calculus and discover a
novel abstract machine definition which, like the calculus, goes "under
lambdas." We prove that machine evaluation is equivalent to standard-order
evaluation. Unlike traditional abstract machines, delimited control plays a
significant role in the machine's behavior. In particular, the machine replaces
the manipulation of a heap using store-based effects with disciplined
management of the evaluation stack using control-based effects. In short, state
is replaced with control. To further articulate this observation, we present a
simulation of call-by-need in a call-by-value language using delimited control
operations
Delimited continuations for Prolog
Delimited continuations are a famous control primitive that originates in the functional programming world. It allows the programmer to suspend and capture the remaining part of a computation in order to resume it later. We put a new Prolog-compatible face on this primitive and specify its semantics by means of a meta-interpreter. Moreover, we establish the power of delimited continuations in Prolog with several example definitions of high-level language features. Finally, we show how to easily and effectively add delimited continuations support to the WAM
Programming with Algebraic Effects and Handlers
Eff is a programming language based on the algebraic approach to
computational effects, in which effects are viewed as algebraic operations and
effect handlers as homomorphisms from free algebras. Eff supports first-class
effects and handlers through which we may easily define new computational
effects, seamlessly combine existing ones, and handle them in novel ways. We
give a denotational semantics of eff and discuss a prototype implementation
based on it. Through examples we demonstrate how the standard effects are
treated in eff, and how eff supports programming techniques that use various
forms of delimited continuations, such as backtracking, breadth-first search,
selection functionals, cooperative multi-threading, and others
On the Static and Dynamic Extents of Delimited Continuations
We show that breadth-first traversal exploits the difference between the static delimited-control operator shift (alias S) and the dynamic delimited-control operator control (alias F). For the last 15 years, this difference has been repeatedly mentioned in the literature but it has only been illustrated with one-line toy examples. Breadth-first traversal fills this vacuum. We also point out where static delimited continuations naturally give rise to the notion of control stack whereas dynamic delimited continuations can be made to account for a notion of `control queue.'
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 Rational Deconstruction of Landin's SECD Machine with the J Operator
Landin's SECD machine was the first abstract machine for applicative
expressions, i.e., functional programs. Landin's J operator was the first
control operator for functional languages, and was specified by an extension of
the SECD machine. We present a family of evaluation functions corresponding to
this extension of the SECD machine, using a series of elementary
transformations (transformation into continu-ation-passing style (CPS) and
defunctionalization, chiefly) and their left inverses (transformation into
direct style and refunctionalization). To this end, we modernize the SECD
machine into a bisimilar one that operates in lockstep with the original one
but that (1) does not use a data stack and (2) uses the caller-save rather than
the callee-save convention for environments. We also identify that the dump
component of the SECD machine is managed in a callee-save way. The caller-save
counterpart of the modernized SECD machine precisely corresponds to Thielecke's
double-barrelled continuations and to Felleisen's encoding of J in terms of
call/cc. We then variously characterize the J operator in terms of CPS and in
terms of delimited-control operators in the CPS hierarchy. As a byproduct, we
also present several reduction semantics for applicative expressions with the J
operator, based on Curien's original calculus of explicit substitutions. These
reduction semantics mechanically correspond to the modernized versions of the
SECD machine and to the best of our knowledge, they provide the first syntactic
theories of applicative expressions with the J operator
An Analytical Approach to Programs as Data Objects
This essay accompanies a selection of 32 articles (referred to in bold face in the text and marginally marked in the bibliographic references) submitted to Aarhus University towards a Doctor Scientiarum degree in Computer Science.The author's previous academic degree, beyond a doctoral degree in June 1986, is an "Habilitation à diriger les recherches" from the Université Pierre et Marie Curie (Paris VI) in France; the corresponding material was submitted in September 1992 and the degree was obtained in January 1993.The present 32 articles have all been written since 1993 and while at DAIMI.Except for one other PhD student, all co-authors are or have been the author's students here in Aarhus
An Approach to Call-by-Name Delimited Continuations
International audienceWe show that a variant of Parigot's λμ-calculus, originally due to de Groote and proved to satisfy Böhm's theorem by Saurin, is canonically interpretable as a call-by-name calculus of delim- ited control. This observation is expressed using Ariola et al's call-by-value calculus of delimited control, an extension of λμ-calculus with delimited control known to be equationally equivalent to Danvy and Filinski's calculus with shift and reset. Our main result then is that de Groote and Saurin's variant of λμ-calculus is equivalent to a canonical call-by-name variant of Ariola et al's calculus. The rest of the paper is devoted to a comparative study of the call-by-name and call-by-value variants of Ariola et al's calculus, covering in particular the questions of simple typing, operational semantics, and continuation-passing-style semantics. Finally, we discuss the relevance of Ariola et al's calculus as a uniform framework for representing different calculi of delimited continuations, including "lazy" variants such as Sabry's shift and lazy reset calculus
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