8 Search Results for "Lhoták, Ondřej"

Document
DOI: 10.4230/LIPIcs.ECOOP.2023.31
Breaking the Negative Cycle: Exploring the Design Space of Stratification for First-Class Datalog Constraints

Authors: Jonathan Lindegaard Starup, Magnus Madsen, and Ondřej Lhoták

Published in: LIPIcs, Volume 263, 37th European Conference on Object-Oriented Programming (ECOOP 2023)

Abstract
The λ_Dat calculus brings together the power of functional and declarative logic programming in one language. In λ_Dat, Datalog constraints are first-class values that can be constructed, passed around as arguments, returned, composed with other constraints, and solved. A significant part of the expressive power of Datalog comes from the use of negation. Stratified negation is a particularly simple and practical form of negation accessible to ordinary programmers. Stratification requires that Datalog programs must not use recursion through negation. For a Datalog program, this requirement is straightforward to check, but for a λ_Dat program, it is not so simple: A λ_Dat program constructs, composes, and solves Datalog programs at runtime. Hence stratification cannot readily be determined at compile-time. In this paper, we explore the design space of stratification for λ_Dat. We investigate strategies to ensure, at compile-time, that programs constructed at runtime are guaranteed to be stratified, and we argue that previous design choices in the Flix programming language have been suboptimal.
Cite as

Jonathan Lindegaard Starup, Magnus Madsen, and Ondřej Lhoták. Breaking the Negative Cycle: Exploring the Design Space of Stratification for First-Class Datalog Constraints. In 37th European Conference on Object-Oriented Programming (ECOOP 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 263, pp. 31:1-31:28, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)

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@InProceedings{starup_et_al:LIPIcs.ECOOP.2023.31,
  author =	{Starup, Jonathan Lindegaard and Madsen, Magnus and Lhot\'{a}k, Ond\v{r}ej},
  title =	{{Breaking the Negative Cycle: Exploring the Design Space of Stratification for First-Class Datalog Constraints}},
  booktitle =	{37th European Conference on Object-Oriented Programming (ECOOP 2023)},
  pages =	{31:1--31:28},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-281-5},
  ISSN =	{1868-8969},
  year =	{2023},
  volume =	{263},
  editor =	{Ali, Karim and Salvaneschi, Guido},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.ECOOP.2023.31},
  URN =		{urn:nbn:de:0030-drops-182244},
  doi =		{10.4230/LIPIcs.ECOOP.2023.31},
  annote =	{Keywords: Datalog, first-class Datalog constraints, negation, stratified negation, type system, row polymorphism, the Flix programming language}
}
Document
Artifact
DOI: 10.4230/DARTS.6.2.10
Blame for Null (Artifact)

Authors: Abel Nieto, Marianna Rapoport, Gregor Richards, and Ondřej Lhoták

Published in: DARTS, Volume 6, Issue 2, Special Issue of the 34th European Conference on Object-Oriented Programming (ECOOP 2020)

Abstract
This artifact is a companion to the paper "Blame for Null", where we formalize multiple calculi to reason about the interoperability between languages where nullability is explicit and those where nullability is implicit. Our main result is a theorem that states that nullability errors can always be blamed on terms with less-precise typing; that is, terms typed as implicitly nullable. We summarize our result with the slogan explicitly nullable programs can't be blamed. The artifact consists of a mechanized Coq proof of the results presented in the paper.
Cite as

Abel Nieto, Marianna Rapoport, Gregor Richards, and Ondřej Lhoták. Blame for Null (Artifact). In Special Issue of the 34th European Conference on Object-Oriented Programming (ECOOP 2020). Dagstuhl Artifacts Series (DARTS), Volume 6, Issue 2, pp. 10:1-10:2, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

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@Article{nieto_et_al:DARTS.6.2.10,
  author =	{Nieto, Abel and Rapoport, Marianna and Richards, Gregor and Lhot\'{a}k, Ond\v{r}ej},
  title =	{{Blame for Null (Artifact)}},
  pages =	{10:1--10:2},
  journal =	{Dagstuhl Artifacts Series},
  ISSN =	{2509-8195},
  year =	{2020},
  volume =	{6},
  number =	{2},
  editor =	{Nieto, Abel and Rapoport, Marianna and Richards, Gregor and Lhot\'{a}k, Ond\v{r}ej},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/DARTS.6.2.10},
  URN =		{urn:nbn:de:0030-drops-132070},
  doi =		{10.4230/DARTS.6.2.10},
  annote =	{Keywords: nullability, type systems, blame calculus, gradual typing}
}
Document
Artifact
DOI: 10.4230/DARTS.6.2.14
Scala with Explicit Nulls (Artifact)

Authors: Abel Nieto, Yaoyu Zhao, Ondřej Lhoták, Angela Chang, and Justin Pu

Published in: DARTS, Volume 6, Issue 2, Special Issue of the 34th European Conference on Object-Oriented Programming (ECOOP 2020)

Abstract
This artifact is a companion to the paper "Scala with Explicit Nulls", where we present a modification to the Scala type system that makes nullability explicit in the types. Specifically, we make reference types non-nullable by default, while still allowing for nullable types via union types. The artifact contains an implementation of this new type system design as a fork of the Dotty (Scala 3) compiler. Additionally, the artifact contains the source code of multiple Scala libraries that we used to evaluate our design.
Cite as

Abel Nieto, Yaoyu Zhao, Ondřej Lhoták, Angela Chang, and Justin Pu. Scala with Explicit Nulls (Artifact). In Special Issue of the 34th European Conference on Object-Oriented Programming (ECOOP 2020). Dagstuhl Artifacts Series (DARTS), Volume 6, Issue 2, pp. 14:1-14:2, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

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@Article{nieto_et_al:DARTS.6.2.14,
  author =	{Nieto, Abel and Zhao, Yaoyu and Lhot\'{a}k, Ond\v{r}ej and Chang, Angela and Pu, Justin},
  title =	{{Scala with Explicit Nulls (Artifact)}},
  pages =	{14:1--14:2},
  journal =	{Dagstuhl Artifacts Series},
  ISSN =	{2509-8195},
  year =	{2020},
  volume =	{6},
  number =	{2},
  editor =	{Nieto, Abel and Zhao, Yaoyu and Lhot\'{a}k, Ond\v{r}ej and Chang, Angela and Pu, Justin},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/DARTS.6.2.14},
  URN =		{urn:nbn:de:0030-drops-132117},
  doi =		{10.4230/DARTS.6.2.14},
  annote =	{Keywords: Scala, Java, nullability, language interoperability, type systems}
}
Document
DOI: 10.4230/LIPIcs.ECOOP.2020.3
Blame for Null

Authors: Abel Nieto, Marianna Rapoport, Gregor Richards, and Ondřej Lhoták

Published in: LIPIcs, Volume 166, 34th European Conference on Object-Oriented Programming (ECOOP 2020)

Abstract
Multiple modern programming languages, including Kotlin, Scala, Swift, and C#, have type systems where nullability is explicitly specified in the types. All of the above also need to interoperate with languages where types remain implicitly nullable, like Java. This leads to runtime errors that can manifest in subtle ways. In this paper, we show how to reason about the presence and provenance of such nullability errors using the concept of blame from gradual typing. Specifically, we introduce a calculus, λ_null, where some terms are typed as implicitly nullable and others as explicitly nullable. Just like in the original blame calculus of Wadler and Findler, interactions between both kinds of terms are mediated by casts with attached blame labels, which indicate the origin of errors. On top of λ_null, we then create a second calculus, λ_null^s, which closely models the interoperability between languages with implicit nullability and languages with explicit nullability, such as Java and Scala. Our main result is a theorem that states that nullability errors in λ_null^s can always be blamed on terms with less-precise typing; that is, terms typed as implicitly nullable. By analogy, this would mean that NullPointerExceptions in combined Java/Scala programs are always the result of unsoundness in the Java type system. We summarize our result with the slogan explicitly nullable programs can't be blamed. All our results are formalized in the Coq proof assistant.
Cite as

Abel Nieto, Marianna Rapoport, Gregor Richards, and Ondřej Lhoták. Blame for Null. In 34th European Conference on Object-Oriented Programming (ECOOP 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 166, pp. 3:1-3:28, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

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@InProceedings{nieto_et_al:LIPIcs.ECOOP.2020.3,
  author =	{Nieto, Abel and Rapoport, Marianna and Richards, Gregor and Lhot\'{a}k, Ond\v{r}ej},
  title =	{{Blame for Null}},
  booktitle =	{34th European Conference on Object-Oriented Programming (ECOOP 2020)},
  pages =	{3:1--3:28},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-154-2},
  ISSN =	{1868-8969},
  year =	{2020},
  volume =	{166},
  editor =	{Hirschfeld, Robert and Pape, Tobias},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.ECOOP.2020.3},
  URN =		{urn:nbn:de:0030-drops-131606},
  doi =		{10.4230/LIPIcs.ECOOP.2020.3},
  annote =	{Keywords: nullability, type systems, blame calculus, gradual typing}
}
Document
DOI: 10.4230/LIPIcs.ECOOP.2020.12
A Semantics for the Essence of React

Authors: Magnus Madsen, Ondřej Lhoták, and Frank Tip

Published in: LIPIcs, Volume 166, 34th European Conference on Object-Oriented Programming (ECOOP 2020)

Abstract
Traditionally, web applications have been written as HTML pages with embedded JavaScript code that implements dynamic and interactive features by manipulating the Document Object Model (DOM) through a low-level browser API. However, this unprincipled approach leads to code that is brittle, difficult to understand, non-modular, and does not facilitate incremental update of user-interfaces in response to state changes. React is a popular framework for constructing web applications that aims to overcome these problems. React applications are written in a declarative and object-oriented style, and consist of components that are organized in a tree structure. Each component has a set of properties representing input parameters, a state consisting of values that may vary over time, and a render method that declaratively specifies the subcomponents of the component. React’s concept of reconciliation determines the impact of state changes and updates the user-interface incrementally by selective mounting and unmounting of subcomponents. At designated points, the React framework invokes lifecycle hooks that enable programmers to perform actions outside the framework such as acquiring and releasing resources needed by a component. These mechanisms exhibit considerable complexity, but, to our knowledge, no formal specification of React’s semantics exists. This paper presents a small-step operational semantics that captures the essence of React, as a first step towards a long-term goal of developing automatic tools for program understanding, automatic testing, and bug finding for React web applications. To demonstrate that key operations such as mounting, unmounting, and reconciliation terminate, we define the notion of a well-behaved component and prove that well-behavedness is preserved by these operations.
Cite as

Magnus Madsen, Ondřej Lhoták, and Frank Tip. A Semantics for the Essence of React. In 34th European Conference on Object-Oriented Programming (ECOOP 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 166, pp. 12:1-12:26, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

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@InProceedings{madsen_et_al:LIPIcs.ECOOP.2020.12,
  author =	{Madsen, Magnus and Lhot\'{a}k, Ond\v{r}ej and Tip, Frank},
  title =	{{A Semantics for the Essence of React}},
  booktitle =	{34th European Conference on Object-Oriented Programming (ECOOP 2020)},
  pages =	{12:1--12:26},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-154-2},
  ISSN =	{1868-8969},
  year =	{2020},
  volume =	{166},
  editor =	{Hirschfeld, Robert and Pape, Tobias},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.ECOOP.2020.12},
  URN =		{urn:nbn:de:0030-drops-131697},
  doi =		{10.4230/LIPIcs.ECOOP.2020.12},
  annote =	{Keywords: JavaScript, React, operational semantics, lifecycle, reconciliation}
}
Document
DOI: 10.4230/LIPIcs.ECOOP.2020.18
Reference Mutability for DOT

Authors: Vlastimil Dort and Ondřej Lhoták

Published in: LIPIcs, Volume 166, 34th European Conference on Object-Oriented Programming (ECOOP 2020)

Abstract
Reference mutability is a type-based technique for controlling mutation that has been thoroughly studied in Java. We explore how reference mutability interacts with the features of Scala by adding it to the Dependent Object Types (DOT) calculus. Our extension shows how reference mutability can be encoded using existing Scala features such as path-dependent, intersection, and union types. We prove type soundness and the immutability guarantee provided by our calculus.
Cite as

Vlastimil Dort and Ondřej Lhoták. Reference Mutability for DOT. In 34th European Conference on Object-Oriented Programming (ECOOP 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 166, pp. 18:1-18:28, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

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@InProceedings{dort_et_al:LIPIcs.ECOOP.2020.18,
  author =	{Dort, Vlastimil and Lhot\'{a}k, Ond\v{r}ej},
  title =	{{Reference Mutability for DOT}},
  booktitle =	{34th European Conference on Object-Oriented Programming (ECOOP 2020)},
  pages =	{18:1--18:28},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-154-2},
  ISSN =	{1868-8969},
  year =	{2020},
  volume =	{166},
  editor =	{Hirschfeld, Robert and Pape, Tobias},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.ECOOP.2020.18},
  URN =		{urn:nbn:de:0030-drops-131755},
  doi =		{10.4230/LIPIcs.ECOOP.2020.18},
  annote =	{Keywords: Reference Mutability, Read-only References, DOT Calculus}
}
Document
DOI: 10.4230/LIPIcs.ECOOP.2020.25
Scala with Explicit Nulls

Authors: Abel Nieto, Yaoyu Zhao, Ondřej Lhoták, Angela Chang, and Justin Pu

Published in: LIPIcs, Volume 166, 34th European Conference on Object-Oriented Programming (ECOOP 2020)

Abstract
The Scala programming language makes all reference types implicitly nullable. This is a problem, because null references do not support most operations that do make sense on regular objects, leading to runtime errors. In this paper, we present a modification to the Scala type system that makes nullability explicit in the types. Specifically, we make reference types non-nullable by default, while still allowing for nullable types via union types. We have implemented this design for explicit nulls as a fork of the Dotty (Scala 3) compiler. We evaluate our scheme by migrating a number of Scala libraries to use explicit nulls. Finally, we give a denotational semantics of type nullification, the interoperability layer between Java and Scala with explicit nulls. We show a soundness theorem stating that, for variants of System F_ω that model Java and Scala, nullification preserves values of types.
Cite as

Abel Nieto, Yaoyu Zhao, Ondřej Lhoták, Angela Chang, and Justin Pu. Scala with Explicit Nulls. In 34th European Conference on Object-Oriented Programming (ECOOP 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 166, pp. 25:1-25:26, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

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@InProceedings{nieto_et_al:LIPIcs.ECOOP.2020.25,
  author =	{Nieto, Abel and Zhao, Yaoyu and Lhot\'{a}k, Ond\v{r}ej and Chang, Angela and Pu, Justin},
  title =	{{Scala with Explicit Nulls}},
  booktitle =	{34th European Conference on Object-Oriented Programming (ECOOP 2020)},
  pages =	{25:1--25:26},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-154-2},
  ISSN =	{1868-8969},
  year =	{2020},
  volume =	{166},
  editor =	{Hirschfeld, Robert and Pape, Tobias},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.ECOOP.2020.25},
  URN =		{urn:nbn:de:0030-drops-131821},
  doi =		{10.4230/LIPIcs.ECOOP.2020.25},
  annote =	{Keywords: Scala, Java, nullability, language interoperability, type systems}
}
Document
DOI: 10.4230/DagRep.3.4.91
Pointer Analysis (Dagstuhl Seminar 13162)

Authors: Ondrej Lhotak, Yannis Smaragdakis, and Manu Sridharan

Published in: Dagstuhl Reports, Volume 3, Issue 4 (2013)

Abstract
This report documents the program and the outcomes of Dagstuhl Seminar 13162 ``Pointer Analysis''. The seminar had 27 attendees, including both pointer analysis experts and researchers developing clients in need of better pointer analysis. The seminar came at a key point in time, with pointer analysis techniques acquiring sophistication but still being just beyond the edge of wide practical deployment. The seminar participants presented recent research results, and identified key open problems and future directions for the field. This report presents abstracts of the participants' talks and summaries of the breakout sessions from the seminar.
Cite as

Ondrej Lhotak, Yannis Smaragdakis, and Manu Sridharan. Pointer Analysis (Dagstuhl Seminar 13162). In Dagstuhl Reports, Volume 3, Issue 4, pp. 91-113, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2013)

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@Article{lhotak_et_al:DagRep.3.4.91,
  author =	{Lhotak, Ondrej and Smaragdakis, Yannis and Sridharan, Manu},
  title =	{{Pointer Analysis (Dagstuhl Seminar 13162)}},
  pages =	{91--113},
  journal =	{Dagstuhl Reports},
  ISSN =	{2192-5283},
  year =	{2013},
  volume =	{3},
  number =	{4},
  editor =	{Lhotak, Ondrej and Smaragdakis, Yannis and Sridharan, Manu},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/DagRep.3.4.91},
  URN =		{urn:nbn:de:0030-drops-41698},
  doi =		{10.4230/DagRep.3.4.91},
  annote =	{Keywords: pointer analysis, points-to analysis, alias analysis, static analysis, programming languages}
}
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