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Documents authored by Uustalu, Tarmo

Document
DOI: 10.4230/LIPIcs.CONCUR.2024.25
A Unifying Categorical View of Nondeterministic Iteration and Tests

Authors: Sergey Goncharov and Tarmo Uustalu

Published in: LIPIcs, Volume 311, 35th International Conference on Concurrency Theory (CONCUR 2024)

Abstract
We study Kleene iteration in the categorical context. A celebrated completeness result by Kozen introduced Kleene algebra (with tests) as a ubiquitous tool for lightweight reasoning about program equivalence, and yet, numerous variants of it came along afterwards to answer the demand for more refined flavors of semantics, such as stateful, concurrent, exceptional, hybrid, branching time, etc. We detach Kleene iteration from Kleene algebra and analyze it from the categorical perspective. The notion, we arrive at is that of Kleene-iteration category (with coproducts and tests), which we show to be general and robust in the sense of compatibility with programming language features, such as exceptions, store, concurrent behaviour, etc. We attest the proposed notion w.r.t. various yardsticks, most importantly, by characterizing the free model as a certain category of (nondeterministic) rational trees.
Cite as

Sergey Goncharov and Tarmo Uustalu. A Unifying Categorical View of Nondeterministic Iteration and Tests. In 35th International Conference on Concurrency Theory (CONCUR 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 311, pp. 25:1-25:22, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{goncharov_et_al:LIPIcs.CONCUR.2024.25,
  author =	{Goncharov, Sergey and Uustalu, Tarmo},
  title =	{{A Unifying Categorical View of Nondeterministic Iteration and Tests}},
  booktitle =	{35th International Conference on Concurrency Theory (CONCUR 2024)},
  pages =	{25:1--25:22},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-339-3},
  ISSN =	{1868-8969},
  year =	{2024},
  volume =	{311},
  editor =	{Majumdar, Rupak and Silva, Alexandra},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CONCUR.2024.25},
  URN =		{urn:nbn:de:0030-drops-207979},
  doi =		{10.4230/LIPIcs.CONCUR.2024.25},
  annote =	{Keywords: Kleene iteration, Elgot iteration, Kleene algebra, coalgebraic resumptions}
}
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.CONCUR.2019.40
Reordering Derivatives of Trace Closures of Regular Languages

Authors: Hendrik Maarand and Tarmo Uustalu

Published in: LIPIcs, Volume 140, 30th International Conference on Concurrency Theory (CONCUR 2019)

Abstract
We provide syntactic derivative-like operations, defined by recursion on regular expressions, in the styles of both Brzozowski and Antimirov, for trace closures of regular languages. Just as the Brzozowski and Antimirov derivative operations for regular languages, these syntactic reordering derivative operations yield deterministic and nondeterministic automata respectively. But trace closures of regular languages are in general not regular, hence these automata cannot generally be finite. Still, as we show, for star-connected expressions, the Antimirov and Brzozowski automata, suitably quotiented, are finite. We also define a refined version of the Antimirov reordering derivative operation where parts-of-derivatives (states of the automaton) are nonempty lists of regular expressions rather than single regular expressions. We define the uniform scattering rank of a language and show that, for a regexp whose language has finite uniform scattering rank, the truncation of the (generally infinite) refined Antimirov automaton, obtained by removing long states, is finite without any quotienting, but still accepts the trace closure. We also show that star-connected languages have finite uniform scattering rank.
Cite as

Hendrik Maarand and Tarmo Uustalu. Reordering Derivatives of Trace Closures of Regular Languages. In 30th International Conference on Concurrency Theory (CONCUR 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 140, pp. 40:1-40:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)

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@InProceedings{maarand_et_al:LIPIcs.CONCUR.2019.40,
  author =	{Maarand, Hendrik and Uustalu, Tarmo},
  title =	{{Reordering Derivatives of Trace Closures of Regular Languages}},
  booktitle =	{30th International Conference on Concurrency Theory (CONCUR 2019)},
  pages =	{40:1--40:16},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-121-4},
  ISSN =	{1868-8969},
  year =	{2019},
  volume =	{140},
  editor =	{Fokkink, Wan and van Glabbeek, Rob},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CONCUR.2019.40},
  URN =		{urn:nbn:de:0030-drops-109426},
  doi =		{10.4230/LIPIcs.CONCUR.2019.40},
  annote =	{Keywords: Mazurkiewicz traces, trace closure, regular languages, finite automata, language derivatives, scattering rank, star-connected expressions}
}
Document
DOI: 10.4230/LIPIcs.FSCD.2019.18
Modal Embeddings and Calling Paradigms

Authors: José Espírito Santo, Luís Pinto, and Tarmo Uustalu

Published in: LIPIcs, Volume 131, 4th International Conference on Formal Structures for Computation and Deduction (FSCD 2019)

Abstract
We study the computational interpretation of the two standard modal embeddings, usually named after Girard and Gödel, of intuitionistic logic into IS4. As source system we take either the call-by-name (cbn) or the call-by-value (cbv) lambda-calculus with simple types. The target system can be taken to be the, arguably, simplest fragment of IS4, here recast as a very simple lambda-calculus equipped with an indeterminate lax monoidal comonad. A slight refinement of the target and of the embeddings shows that: the target is a calculus indifferent to the calling paradigms cbn/cbv, obeying a new paradigm that we baptize call-by-box (cbb), and enjoying standardization; and that Girard’s (resp. Gödel’s) embbedding is a translation of cbn (resp. cbv) lambda-calculus into this calculus, using a compilation technique we call protecting-by-a-box, enjoying the preservation and reflection properties known for cps translations - but in a stronger form that allows the extraction of standardization for cbn or cbv as consequence of standardization for cbb. The modal target and embeddings achieve thus an unification of call-by-name and call-by-value as call-by-box.
Cite as

José Espírito Santo, Luís Pinto, and Tarmo Uustalu. Modal Embeddings and Calling Paradigms. In 4th International Conference on Formal Structures for Computation and Deduction (FSCD 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 131, pp. 18:1-18:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)

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@InProceedings{espiritosanto_et_al:LIPIcs.FSCD.2019.18,
  author =	{Esp{\'\i}rito Santo, Jos\'{e} and Pinto, Lu{\'\i}s and Uustalu, Tarmo},
  title =	{{Modal Embeddings and Calling Paradigms}},
  booktitle =	{4th International Conference on Formal Structures for Computation and Deduction (FSCD 2019)},
  pages =	{18:1--18:20},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-107-8},
  ISSN =	{1868-8969},
  year =	{2019},
  volume =	{131},
  editor =	{Geuvers, Herman},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.FSCD.2019.18},
  URN =		{urn:nbn:de:0030-drops-105256},
  doi =		{10.4230/LIPIcs.FSCD.2019.18},
  annote =	{Keywords: intuitionistic S4, call-by-name, call-by-value, comonadic lambda-calculus, standardization, indifference property}
}
Document
Complete Volume
DOI: 10.4230/LIPIcs.TYPES.2015
LIPIcs, Volume 69, TYPES'15, Complete Volume

Authors: Tarmo Uustalu

Published in: LIPIcs, Volume 69, 21st International Conference on Types for Proofs and Programs (TYPES 2015) (2018)

Abstract
LIPIcs, Volume 69, TYPES'15, Complete Volume
Cite as

21st International Conference on Types for Proofs and Programs (TYPES 2015). Leibniz International Proceedings in Informatics (LIPIcs), Volume 69, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)

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@Proceedings{uustalu:LIPIcs.TYPES.2015,
  title =	{{LIPIcs, Volume 69, TYPES'15, Complete Volume}},
  booktitle =	{21st International Conference on Types for Proofs and Programs (TYPES 2015)},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-030-9},
  ISSN =	{1868-8969},
  year =	{2018},
  volume =	{69},
  editor =	{Uustalu, Tarmo},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.TYPES.2015},
  URN =		{urn:nbn:de:0030-drops-86220},
  doi =		{10.4230/LIPIcs.TYPES.2015},
  annote =	{Keywords: Mathematical Logic and Formal Languages: Mathematical Logic - Lambda calculus and related systems}
}
Document
Front Matter
DOI: 10.4230/LIPIcs.TYPES.2015.0
Front Matter, Table of Contents, Preface, External Reviewers

Authors: Tarmo Uustalu

Published in: LIPIcs, Volume 69, 21st International Conference on Types for Proofs and Programs (TYPES 2015) (2018)

Abstract
Front Matter, Table of Contents, Preface, External Reviewers
Cite as

21st International Conference on Types for Proofs and Programs (TYPES 2015). Leibniz International Proceedings in Informatics (LIPIcs), Volume 69, pp. 0:i-0:xii, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)

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@InProceedings{uustalu:LIPIcs.TYPES.2015.0,
  author =	{Uustalu, Tarmo},
  title =	{{Front Matter, Table of Contents, Preface, External Reviewers}},
  booktitle =	{21st International Conference on Types for Proofs and Programs (TYPES 2015)},
  pages =	{0:i--0:xii},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-030-9},
  ISSN =	{1868-8969},
  year =	{2018},
  volume =	{69},
  editor =	{Uustalu, Tarmo},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.TYPES.2015.0},
  URN =		{urn:nbn:de:0030-drops-84704},
  doi =		{10.4230/LIPIcs.TYPES.2015.0},
  annote =	{Keywords: Front Matter, Table of Contents, Preface, External Reviewers}
}
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.
Cite as

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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