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Scalable Handling of Effects (Dagstuhl Seminar 21292)

Authors: Danel Ahman, Amal Ahmed, Sam Lindley, and Andreas Rossberg

Published in: Dagstuhl Reports, Volume 11, Issue 6 (2021)

Abstract

Built on solid mathematical foundations, effect handlers offer a uniform and elegant approach to programming with user-defined computational effects. They subsume many widely used programming concepts and abstractions, such as actors, async/await, backtracking, coroutines, generators/iterators, and probabilistic programming. As such, they allow language implementers to target a single implementation of effect handlers, freeing language implementers from having to maintain separate ad hoc implementations of each of the features listed above. Due to their wide applicability, effect handlers are enjoying growing interest in academia and industry. For instance, several effect handler oriented research languages are under active development (such as Eff, Frank, and Koka), as are effect handler libraries for mainstream languages (such as C and Java), effect handlers are seeing increasing use in probabilistic programming tools (such as Uber’s Pyro), and proposals are in the pipeline to include them natively in low-level languages (such as WebAssembly). Effect handlers are also a key part of Multicore OCaml, which incorporates an efficient implementation of them for uniformly expressing user-definable concurrency models in the language. However, enabling effect handlers to scale requires tackling some hard problems, both in theory and in practice. Inspired by experience of developing, programming with, and reasoning about effect handlers in practice, we identify five key problem areas to be addressed at this Dagstuhl Seminar in order to enable effect handlers to scale: Safety, Modularity, Interoperability, Legibility, and Efficiency. In particular, we seek answers to the following questions: - How can we enforce safe interaction between effect handler programs and external resources? - How can we enable modular use of effect handlers for programming in the large? - How can we support interoperable effect handler programs written in different languages? - How can we write legible effect handler programs in a style accessible to mainstream programmers? - How can we generate efficient code from effect handler programs?

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Danel Ahman, Amal Ahmed, Sam Lindley, and Andreas Rossberg. Scalable Handling of Effects (Dagstuhl Seminar 21292). In Dagstuhl Reports, Volume 11, Issue 6, pp. 54-81, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)

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@Article{ahman_et_al:DagRep.11.6.54,
  author =	{Ahman, Danel and Ahmed, Amal and Lindley, Sam and Rossberg, Andreas},
  title =	{{Scalable Handling of Effects (Dagstuhl Seminar 21292)}},
  pages =	{54--81},
  journal =	{Dagstuhl Reports},
  ISSN =	{2192-5283},
  year =	{2021},
  volume =	{11},
  number =	{6},
  editor =	{Ahman, Danel and Ahmed, Amal and Lindley, Sam and Rossberg, Andreas},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/DagRep.11.6.54},
  URN =		{urn:nbn:de:0030-drops-155800},
  doi =		{10.4230/DagRep.11.6.54},
  annote =	{Keywords: continuations, Effect handlers, Wasm}
}

Document

DOI: 10.4230/LIPIcs.CALCO.2019.14

Decomposing Comonad Morphisms

Authors: Danel Ahman and Tarmo Uustalu

Published in: LIPIcs, Volume 139, 8th Conference on Algebra and Coalgebra in Computer Science (CALCO 2019)

Abstract

The analysis of set comonads whose underlying functor is a container functor in terms of directed containers makes it a simple observation that any morphism between two such comonads factors through a third one by two comonad morphisms, whereof the first is identity on shapes and the second is identity on positions in every shape. This observation turns out to generalize into a much more involved result about comonad morphisms to comonads whose underlying functor preserves Cartesian natural transformations to itself on any category with finite limits. The bijection between comonad coalgebras and comonad morphisms from costate comonads thus also yields a decomposition of comonad coalgebras.

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Danel Ahman and Tarmo Uustalu. Decomposing Comonad Morphisms. In 8th Conference on Algebra and Coalgebra in Computer Science (CALCO 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 139, pp. 14:1-14:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)

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@InProceedings{ahman_et_al:LIPIcs.CALCO.2019.14,
  author =	{Ahman, Danel and Uustalu, Tarmo},
  title =	{{Decomposing Comonad Morphisms}},
  booktitle =	{8th Conference on Algebra and Coalgebra in Computer Science (CALCO 2019)},
  pages =	{14:1--14:19},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-120-7},
  ISSN =	{1868-8969},
  year =	{2019},
  volume =	{139},
  editor =	{Roggenbach, Markus and Sokolova, Ana},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CALCO.2019.14},
  URN =		{urn:nbn:de:0030-drops-114427},
  doi =		{10.4230/LIPIcs.CALCO.2019.14},
  annote =	{Keywords: container functors (polynomial functors), container comonads, comonad morphisms and comonad coalgebras, cofunctors, lenses}
}

Document

DOI: 10.4230/LIPIcs.TYPES.2013.1

Update Monads: Cointerpreting Directed Containers

Authors: Danel Ahman and Tarmo Uustalu

Published in: LIPIcs, Volume 26, 19th International Conference on Types for Proofs and Programs (TYPES 2013)

Abstract

We introduce update monads as a generalization of state monads. Update monads are the compatible compositions of reader and writer monads given by a set and a monoid. Distributive laws between such monads are given by actions of the monoid on the set. We also discuss a dependently typed generalization of update monads. Unlike simple update monads, they cannot be factored into a reader and writer monad, but rather into similarly looking relative monads. Dependently typed update monads arise from cointerpreting directed containers, by which we mean an extension of an interpretation of the opposite of the category of containers into the category of set functors.

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Danel Ahman and Tarmo Uustalu. Update Monads: Cointerpreting Directed Containers. In 19th International Conference on Types for Proofs and Programs (TYPES 2013). Leibniz International Proceedings in Informatics (LIPIcs), Volume 26, pp. 1-23, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2014)

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@InProceedings{ahman_et_al:LIPIcs.TYPES.2013.1,
  author =	{Ahman, Danel and Uustalu, Tarmo},
  title =	{{Update Monads: Cointerpreting Directed Containers}},
  booktitle =	{19th International Conference on Types for Proofs and Programs (TYPES 2013)},
  pages =	{1--23},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-939897-72-9},
  ISSN =	{1868-8969},
  year =	{2014},
  volume =	{26},
  editor =	{Matthes, Ralph and Schubert, Aleksy},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.TYPES.2013.1},
  URN =		{urn:nbn:de:0030-drops-46235},
  doi =		{10.4230/LIPIcs.TYPES.2013.1},
  annote =	{Keywords: monads and distributive laws, reader, writer and state monads, monoids and monoid actions, directed containers}
}

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Documents authored by Ahman, Danel

Scalable Handling of Effects (Dagstuhl Seminar 21292)

Abstract

Cite as

Decomposing Comonad Morphisms

Abstract

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Update Monads: Cointerpreting Directed Containers

Abstract

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