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Pearl

DOI: 10.4230/LIPIcs.ECOOP.2019.24

Julia’s Efficient Algorithm for Subtyping Unions and Covariant Tuples (Pearl)

Authors: Benjamin Chung, Francesco Zappa Nardelli, and Jan Vitek

Published in: LIPIcs, Volume 134, 33rd European Conference on Object-Oriented Programming (ECOOP 2019)

Abstract

The Julia programming language supports multiple dispatch and provides a rich type annotation language to specify method applicability. When multiple methods are applicable for a given call, Julia relies on subtyping between method signatures to pick the correct method to invoke. Julia’s subtyping algorithm is surprisingly complex, and determining whether it is correct remains an open question. In this paper, we focus on one piece of this problem: the interaction between union types and covariant tuples. Previous work normalized unions inside tuples to disjunctive normal form. However, this strategy has two drawbacks: complex type signatures induce space explosion, and interference between normalization and other features of Julia’s type system. In this paper, we describe the algorithm that Julia uses to compute subtyping between tuples and unions - an algorithm that is immune to space explosion and plays well with other features of the language. We prove this algorithm correct and complete against a semantic-subtyping denotational model in Coq.

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Benjamin Chung, Francesco Zappa Nardelli, and Jan Vitek. Julia’s Efficient Algorithm for Subtyping Unions and Covariant Tuples (Pearl). In 33rd European Conference on Object-Oriented Programming (ECOOP 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 134, pp. 24:1-24:15, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)

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@InProceedings{chung_et_al:LIPIcs.ECOOP.2019.24,
  author =	{Chung, Benjamin and Zappa Nardelli, Francesco and Vitek, Jan},
  title =	{{Julia’s Efficient Algorithm for Subtyping Unions and Covariant Tuples}},
  booktitle =	{33rd European Conference on Object-Oriented Programming (ECOOP 2019)},
  pages =	{24:1--24:15},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-111-5},
  ISSN =	{1868-8969},
  year =	{2019},
  volume =	{134},
  editor =	{Donaldson, Alastair F.},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ECOOP.2019.24},
  URN =		{urn:nbn:de:0030-drops-108165},
  doi =		{10.4230/LIPIcs.ECOOP.2019.24},
  annote =	{Keywords: Type systems, Subtyping, Union types}
}

Document

DOI: 10.4230/LIPIcs.ECOOP.2018.12

KafKa: Gradual Typing for Objects

Authors: Benjamin Chung, Paley Li, Francesco Zappa Nardelli, and Jan Vitek

Published in: LIPIcs, Volume 109, 32nd European Conference on Object-Oriented Programming (ECOOP 2018)

Abstract

A wide range of gradual type systems have been proposed, providing many languages with the ability to mix typed and untyped code. However, hiding under language details, these gradual type systems embody fundamentally different ideas of what it means to be well-typed. In this paper, we show that four of the most common gradual type systems provide distinct guarantees, and we give a formal framework for comparing gradual type systems for object-oriented languages. First, we show that the different gradual type systems are practically distinguishable via a three-part litmus test. We present a formal framework for defining and comparing gradual type systems. Within this framework, different gradual type systems become translations between a common source and target language, allowing for direct comparison of semantics and guarantees.

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Benjamin Chung, Paley Li, Francesco Zappa Nardelli, and Jan Vitek. KafKa: Gradual Typing for Objects. In 32nd European Conference on Object-Oriented Programming (ECOOP 2018). Leibniz International Proceedings in Informatics (LIPIcs), Volume 109, pp. 12:1-12:25, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)

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@InProceedings{chung_et_al:LIPIcs.ECOOP.2018.12,
  author =	{Chung, Benjamin and Li, Paley and Zappa Nardelli, Francesco and Vitek, Jan},
  title =	{{KafKa: Gradual Typing for Objects}},
  booktitle =	{32nd European Conference on Object-Oriented Programming (ECOOP 2018)},
  pages =	{12:1--12:25},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-079-8},
  ISSN =	{1868-8969},
  year =	{2018},
  volume =	{109},
  editor =	{Millstein, Todd},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ECOOP.2018.12},
  URN =		{urn:nbn:de:0030-drops-92170},
  doi =		{10.4230/LIPIcs.ECOOP.2018.12},
  annote =	{Keywords: Gradual typing, object-orientation, language design, type systems}
}

Document

DOI: 10.4230/LIPIcs.ECOOP.2015.76

Concrete Types for TypeScript

Authors: Gregor Richards, Francesco Zappa Nardelli, and Jan Vitek

Published in: LIPIcs, Volume 37, 29th European Conference on Object-Oriented Programming (ECOOP 2015)

Abstract

Typescript extends JavaScript with optional type annotations that are, by design, unsound and, that the Typescript compiler discards as it emits code. This design point preserves programming idioms developers are familiar with, and allows them to leave their legacy code unchanged, while offering a measure of static error checking in parts of the program that have type annotations. We present an alternative design for TypeScript, one where it is possible to support the same degree of dynamism, but where types can be strengthened to provide hard guarantees. We report on an implementation, called StrongScript, that improves runtime performance of typed programs when run on a modified version of the V8 JavaScript engine.

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Gregor Richards, Francesco Zappa Nardelli, and Jan Vitek. Concrete Types for TypeScript. In 29th European Conference on Object-Oriented Programming (ECOOP 2015). Leibniz International Proceedings in Informatics (LIPIcs), Volume 37, pp. 76-100, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2015)

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@InProceedings{richards_et_al:LIPIcs.ECOOP.2015.76,
  author =	{Richards, Gregor and Zappa Nardelli, Francesco and Vitek, Jan},
  title =	{{Concrete Types for TypeScript}},
  booktitle =	{29th European Conference on Object-Oriented Programming (ECOOP 2015)},
  pages =	{76--100},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-939897-86-6},
  ISSN =	{1868-8969},
  year =	{2015},
  volume =	{37},
  editor =	{Boyland, John Tang},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ECOOP.2015.76},
  URN =		{urn:nbn:de:0030-drops-52185},
  doi =		{10.4230/LIPIcs.ECOOP.2015.76},
  annote =	{Keywords: Gradual typing, dynamic languages}
}

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Documents authored by Zappa Nardelli, Francesco

Julia’s Efficient Algorithm for Subtyping Unions and Covariant Tuples (Pearl)

Abstract

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KafKa: Gradual Typing for Objects

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Concrete Types for TypeScript

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