Effects for efficiency: asymptotic speedup with first-class control

Hillerström, Daniel; Lindley, Sam; Longley, John

doi:10.1145/3408982

Cited by 3 publications

(1 citation statement)

References 34 publications

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“…Algebraic effects and their handlers have emerged as a convenient way to control impure behaviour. They are built upon a strong mathematical foundation (Plotkin and Pretnar, 2009;Plotkin and Power, 2003), their semantics can be precisely defined (Kammar et al, 2013), and in some cases they provide an improvement in runtime complexity compared to pure languages (Hillerström et al, 2020). While providing a useful formal framework for reasoning about side effects, algebraic effects and handlers have also proved to be an increasingly convenient modular abstraction that has been adopted across many disciplines.…”

Section: Effects and Effect Handlingmentioning

confidence: 99%

Probabilistic programming with densities in SlicStan: efficient, flexible, and deterministic

Gorinova

Gordon

Sutton

2019

Proc. ACM Program. Lang.

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Stan is a probabilistic programming language that has been increasingly used for real-world scalable projects. However, to make practical inference possible, the language sacrifices some of its usability by adopting a block syntax, which lacks compositionality and flexible user-defined functions. Moreover, the semantics of the language has been mainly given in terms of intuition about implementation, and has not been formalised.This paper provides a formal treatment of the Stan language, and introduces the probabilistic programming language SlicStan -a compositional, self-optimising version of Stan. Our main contributions are (1) the formalisation of a core subset of Stan through an operational density-based semantics; (2) the design and semantics of the Stan-like language SlicStan, which facilities better code reuse and abstraction through its compositional syntax, more flexible functions, and information-flow type system; and (3) a formal, semanticpreserving procedure for translating SlicStan to Stan.

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Section: Effects and Effect Handlingmentioning

confidence: 99%

Probabilistic programming with densities in SlicStan: efficient, flexible, and deterministic

Gorinova

Gordon

Sutton

2019

Proc. ACM Program. Lang.

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Asymptotic speedup via effect handlers

HILLERSTRÖM,

LINDLEY,

LONGLEY

2024

J. Funct. Prog.

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We study a fundamental efficiency benefit afforded by delimited control, showing that for certain higher-order functions, a language with advanced control features offers an asymptotic improvement in runtime over a language without them. Specifically, we consider the generic count problem in the context of a pure functional base language ${\lambda_{\textrm{b}}}$ and an extension ${\lambda_{\textrm{h}}}$ with general effect handlers. We prove that ${\lambda_{\textrm{h}}}$ admits an asymptotically more efficient implementation of generic count than any implementation in ${\lambda_{\textrm{b}}}$ . We also show that this gap remains even when ${\lambda_{\textrm{b}}}$ is extended to a language ${{{{{{\lambda_{\textrm{a}}}}}}}}$ with affine effect handlers, which is strong enough to encode exceptions, local state, coroutines and single-shot continuations. This locates the efficiency difference in the gap between ‘single-shot’ and ‘multi-shot’ versions of delimited control. To our knowledge, these results are the first of their kind for control operators.

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Soundly Handling Linearity

Tang,

Hillerström,

Lindley

et al. 2024

Proc. ACM Program. Lang.

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We propose a novel approach to soundly combining linear types with multi-shot effect handlers. circear type systems statically ensure that resources such as file handles and communication channels are used exactly once. Effect handlers provide a rich modular programming abstraction for implementing features ranging from exceptions to concurrency to backtracking. Whereas conventional linear type systems bake in the assumption that continuations are invoked exactly once, effect handlers allow continuations to be discarded (e.g. for exceptions) or invoked more than once (e.g. for backtracking). This mismatch leads to soundness bugs in existing systems such as the programming language Links, which combines linearity (for session types) with effect handlers. We introduce control-flow linearity as a means to ensure that continuations are used in accordance with the linearity of any resources they capture, ruling out such soundness bugs. We formalise the notion of control-flow linearity in a System F-style core calculus F eff ∘ equipped with linear types, an effect type system, and effect handlers. We define a linearity-aware semantics in order to formally prove that F eff ∘ preserves the integrity of linear values in the sense that no linear value is discarded or duplicated. In order to show that control-flow linearity can be made practical, we adapt circks based on the design of F eff ∘ , in doing so fixing a long-standing soundness bug. Finally, to better expose the potential of control-flow linearity, we define an ML-style core calculus Q eff ∘ , based on qualified types, which requires no programmer provided annotations, and instead relies entirely on type inference to infer control-flow linearity. Both linearity and effects are captured by qualified types. Q eff ∘ overcomes a number of practical limitations of F eff ∘ , supporting abstraction over linearity, linearity dependencies between type variables, and a much more fine-grained notion of control-flow linearity.

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Effects for efficiency: asymptotic speedup with first-class control

Cited by 3 publications

References 34 publications

Probabilistic programming with densities in SlicStan: efficient, flexible, and deterministic

Probabilistic programming with densities in SlicStan: efficient, flexible, and deterministic

Asymptotic speedup via effect handlers

Soundly Handling Linearity

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