Shallow Effect Handlers

Hillerström, Daniel; Lindley, Sam

doi:10.1007/978-3-030-02768-1_22

Cited by 30 publications

(22 citation statements)

References 22 publications

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“…Relation to Prior Publications This paper combines and streamlines the main results of three previously published papers Hillerström et al, 2017;Hillerström & Lindley, 2018). We have improved the CPS translations described by Hillerström et al (2017) and Hillerström & Lindley (2018) to remove all administrative reductions, and fixed a minor bug in the implementation of shallow handlers (Section 5). The abstract machine described by has been extended to also implement shallow handlers.…”

Section: Introductionmentioning

confidence: 74%

“…In this section, we present λ † , a Church-style row-polymorphic call-by-value calculus with effect handlers (Hillerström & Lindley, 2018). The calculus captures the essence of the effect handlers as realised by the intermediate representation of Links.…”

Section: Handler Calculusmentioning

confidence: 99%

“…However, there is a payoff in the removal of administrative reductions at run time. The translations presented by Hillerström et al (2017) and Hillerström & Lindley (2018) did not do this decomposition and repackaging step, which resulted in additional administrative reductions in the translation due to the translations of let and do being passed dynamic continuations when they were expecting statically known ones.…”

Section: The Translationmentioning

confidence: 99%

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Effect handlers via generalised continuations

Hillerström¹,

Lindley

Atkey³

2020

J. Funct. Prog.

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Plotkin and Pretnar’s effect handlers offer a versatile abstraction for modular programming with user-defined effects. This paper focuses on foundations for implementing effect handlers, for the three different kinds of effect handlers that have been proposed in the literature: deep, shallow, and parameterised. Traditional deep handlers are defined by folds over computation trees and are the original construct proposed by Plotkin and Pretnar. Shallow handlers are defined by case splits (rather than folds) over computation trees. Parameterised handlers are deep handlers extended with a state value that is threaded through the folds over computation trees. We formulate the extensions both directly and via encodings in terms of deep handlers and illustrate how the direct implementations avoid the generation of unnecessary closures. We give two distinct foundational implementations of all the kinds of handlers we consider: a continuation-passing style (CPS) transformation and a CEK-style abstract machine. In both cases, the key ingredient is a generalisation of the notion of continuation to accommodate stacks of effect handlers. We obtain our CPS translation through a series of refinements as follows. We begin with a first-order CPS translation into untyped lambda calculus which manages a stack of continuations and handlers as a curried sequence of arguments. We then refine the initial CPS translation by uncurrying it to yield a properly tail-recursive translation and then moving towards more and more intensional representations of continuations in order to support different kinds of effect handlers. Finally, we make the translation higher order in order to contract administrative redexes at translation time. Our abstract machine design then uses the same generalised continuation representation as the CPS translation. We have implemented both the abstract machine and the CPS transformation (plus extensions) as backends for the Links web programming language.

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Section: Introductionmentioning

confidence: 74%

Section: Handler Calculusmentioning

confidence: 99%

Section: The Translationmentioning

confidence: 99%

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Effect handlers via generalised continuations

Hillerström¹,

Lindley

Atkey³

2020

J. Funct. Prog.

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“…Second, shallow handlers do not resume under their own handler and as a result generally resume under a different handler context than they captured. Fortunately, any program with shallow handler can be expressed with deep handlers as well [Hillerström and Lindley 2018;Kammar et al 2013] and thus avoid the unscoped resumptions. Finally, Kiselyov et al [2006] show an example of code migration that resumes locally captured continuations on another host, possibly under different handlers.…”

Section: Expressivenessmentioning

confidence: 99%

Effect handlers, evidently

Xie

Brachthäuser

Hillerström

et al. 2020

Proc. ACM Program. Lang.

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Algebraic effect handlers are a powerful way to incorporate effects in a programming language. Sometimes perhaps even too powerful. In this article we define a restriction of general effect handlers with scoped resumptions. We argue one can still express all important effects, while improving reasoning about effect handlers. Using the newly gained guarantees, we define a sound and coherent evidence translation for effect handlers, which directly passes the handlers as evidence to each operation. We prove full soundness and coherence of the translation into plain lambda calculus. The evidence in turn enables efficient implementations of effect operations; in particular, we show we can execute tail-resumptive operations in place (without needing to capture the evaluation context), and how we can replace the runtime search for a handler by indexing with a constant offset. CCS Concepts: • Software and its engineering → Control structures; Polymorphism; • Theory of computation → Type theory.

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“…As witnessed by the work of Hillerström and Lindley [2018] the machine structures are readily realisable using standard persistent functional data structures. Pure continuations on the base machine and generalised continuations on the handler machine can be implemented using linked lists with a time complexity of O(1) for the extension operation (_ :: _).…”

Section: Realisability and Asymptotic Complexitymentioning

confidence: 99%

Effects for efficiency: asymptotic speedup with first-class control

Hillerström

Lindley

Longley

2020

Proc. ACM Program. Lang.

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We study the fundamental efficiency of delimited control. Specifically, we show that effect handlers enable an asymptotic improvement in runtime complexity for a certain class of functions. We consider the generic count problem using a pure PCF-like base language λ b and its extension with effect handlers λ h. We show that λ h admits an asymptotically more efficient implementation of generic count than any λ b implementation. We also show that this efficiency gap remains when λ b is extended with mutable state. To our knowledge this result is the first of its kind for control operators.

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Shallow Effect Handlers

Cited by 30 publications

References 22 publications

Effect handlers via generalised continuations

Effect handlers via generalised continuations

Effect handlers, evidently

Effects for efficiency: asymptotic speedup with first-class control

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