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Artifact
Union Types with Disjoint Switches (Artifact)

Authors: Baber Rehman, Xuejing Huang, Ningning Xie, and Bruno C. d. S. Oliveira

Published in: DARTS, Volume 8, Issue 2, Special Issue of the 36th European Conference on Object-Oriented Programming (ECOOP 2022)


Abstract
This artifact contains the mechanical formalization of the calculi associated with the paper Union Types with Disjoint Switches. All of the metatheory has been formalized in Coq theorem prover. We provide a docker image as well the code archive. The paper studies a union calculus ({λ_{u}}). Primary idea of {λ_{u}} calculus is a type based disjoint switch construct for the elimination of union types. We also study several extensions of the {λ_{u}} calculus including intersection types, distributive subtyping, nominal types, parametric polymorphism and an extension for the empty types.

Cite as

Baber Rehman, Xuejing Huang, Ningning Xie, and Bruno C. d. S. Oliveira. Union Types with Disjoint Switches (Artifact). In Special Issue of the 36th European Conference on Object-Oriented Programming (ECOOP 2022). Dagstuhl Artifacts Series (DARTS), Volume 8, Issue 2, pp. 17:1-17:6, Schloss Dagstuhl - Leibniz-Zentrum für Informatik (2022)


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@Article{rehman_et_al:DARTS.8.2.17,
  author =	{Rehman, Baber and Huang, Xuejing and Xie, Ningning and Oliveira, Bruno C. d. S.},
  title =	{{Union Types with Disjoint Switches (Artifact)}},
  pages =	{17:1--17:6},
  journal =	{Dagstuhl Artifacts Series},
  ISSN =	{2509-8195},
  year =	{2022},
  volume =	{8},
  number =	{2},
  editor =	{Rehman, Baber and Huang, Xuejing and Xie, Ningning and Oliveira, Bruno C. d. S.},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/DARTS.8.2.17},
  URN =		{urn:nbn:de:0030-drops-162150},
  doi =		{10.4230/DARTS.8.2.17},
  annote =	{Keywords: Union types, switch expression, disjointness, intersection types}
}
Document
Union Types with Disjoint Switches

Authors: Baber Rehman, Xuejing Huang, Ningning Xie, and Bruno C. d. S. Oliveira

Published in: LIPIcs, Volume 222, 36th European Conference on Object-Oriented Programming (ECOOP 2022)


Abstract
Union types are nowadays a common feature in many modern programming languages. This paper investigates a formulation of union types with an elimination construct that enables case analysis (or switches) on types. The interesting aspect of this construct is that each clause must operate on disjoint types. By using disjoint switches, it is possible to ensure exhaustiveness (i.e. all possible cases are handled), and that none of the cases overlap. In turn, this means that the order of the cases does not matter and that reordering the cases has no impact on the semantics, helping with program understanding and refactoring. While implemented in the Ceylon language, disjoint switches have not been formally studied in the research literature, although a related notion of disjointness has been studied in the context of disjoint intersection types. We study union types with disjoint switches formally and in a language independent way. We first present a simplified calculus, called the union calculus (λ_u), which includes disjoint switches and prove several results, including type soundness and determinism. The notion of disjointness in λ_u is in essence the dual notion of disjointness for intersection types. We then present a more feature-rich formulation of λ_u, which includes intersection types, distributive subtyping and a simple form of nominal types. This extension reveals new challenges. Those challenges require us to depart from the dual notion of disjointness for intersection types, and use a more general formulation of disjointness instead. Among other applications, we show that disjoint switches provide an alternative to certain forms of overloading, and that they enable a simple approach to nullable (or optional) types. All the results about λ_u and its extensions have been formalized in the Coq theorem prover.

Cite as

Baber Rehman, Xuejing Huang, Ningning Xie, and Bruno C. d. S. Oliveira. Union Types with Disjoint Switches. In 36th European Conference on Object-Oriented Programming (ECOOP 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 222, pp. 25:1-25:31, Schloss Dagstuhl - Leibniz-Zentrum für Informatik (2022)


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@InProceedings{rehman_et_al:LIPIcs.ECOOP.2022.25,
  author =	{Rehman, Baber and Huang, Xuejing and Xie, Ningning and Oliveira, Bruno C. d. S.},
  title =	{{Union Types with Disjoint Switches}},
  booktitle =	{36th European Conference on Object-Oriented Programming (ECOOP 2022)},
  pages =	{25:1--25:31},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-225-9},
  ISSN =	{1868-8969},
  year =	{2022},
  volume =	{222},
  editor =	{Ali, Karim and Vitek, Jan},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ECOOP.2022.25},
  URN =		{urn:nbn:de:0030-drops-162531},
  doi =		{10.4230/LIPIcs.ECOOP.2022.25},
  annote =	{Keywords: Union types, switch expression, disjointness, intersection types}
}
Document
Artifact
The Duality of Subtyping (Artifact)

Authors: Bruno C. d. S. Oliveira, Cui Shaobo, and Baber Rehman

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


Abstract
This artifact contains the Coq formalization associated with the paper The Duality of Subtyping submitted in ECOOP 2020. This document explains how to run the Coq formalization. Artifact can either be compiled in the pre-built docker image with all the dependencies installed or it could be built from the scratch. Sections 1-7 explain the basic information about the artifact. Section A explains how to get the docker image for the artifact. Section B explains the prerequisites and the steps to run coq files from scratch. Section C explains coq files briefly. Section D shows the correspondence between important lemmas discussed in paper and their respective Coq formalization. The term MonoTyping used in artifact corresponds to the standard subtyping systems.

Cite as

Bruno C. d. S. Oliveira, Cui Shaobo, and Baber Rehman. The Duality of Subtyping (Artifact). In Special Issue of the 34th European Conference on Object-Oriented Programming (ECOOP 2020). Dagstuhl Artifacts Series (DARTS), Volume 6, Issue 2, pp. 8:1-8:6, Schloss Dagstuhl - Leibniz-Zentrum für Informatik (2020)


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@Article{oliveira_et_al:DARTS.6.2.8,
  author =	{Oliveira, Bruno C. d. S. and Shaobo, Cui and Rehman, Baber},
  title =	{{The Duality of Subtyping (Artifact)}},
  pages =	{8:1--8:6},
  journal =	{Dagstuhl Artifacts Series},
  ISSN =	{2509-8195},
  year =	{2020},
  volume =	{6},
  number =	{2},
  editor =	{Oliveira, Bruno C. d. S. and Shaobo, Cui and Rehman, Baber},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/DARTS.6.2.8},
  URN =		{urn:nbn:de:0030-drops-132051},
  doi =		{10.4230/DARTS.6.2.8},
  annote =	{Keywords: DuoTyping, OOP, Duality, Subtyping, Supertyping}
}
Document
The Duality of Subtyping

Authors: Bruno C. d. S. Oliveira, Cui Shaobo, and Baber Rehman

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


Abstract
Subtyping is a concept frequently encountered in many programming languages and calculi. Various forms of subtyping exist for different type system features, including intersection types, union types or bounded quantification. Normally these features are designed independently of each other, without exploiting obvious similarities (or dualities) between features. This paper proposes a novel methodology for designing subtyping relations that exploits duality between features. At the core of our methodology is a generalization of subtyping relations, which we call Duotyping. Duotyping is parameterized by the mode of the relation. One of these modes is the usual subtyping, while another mode is supertyping (the dual of subtyping). Using the mode it is possible to generalize the usual rules of subtyping to account not only for the intended behaviour of one particular language construct, but also of its dual. Duotyping brings multiple benefits, including: shorter specifications and implementations, dual features that come essentially for free, as well as new proof techniques for various properties of subtyping. To evaluate a design based on Duotyping against traditional designs, we formalized various calculi with common OOP features (including union types, intersection types and bounded quantification) in Coq in both styles. Our results show that the metatheory when using Duotyping does not come at a significant cost: the metatheory with Duotyping has similar complexity and size compared to the metatheory for traditional designs. However, we discover new features as duals to well-known features. Furthermore, we also show that Duotyping can significantly simplify transitivity proofs for many of the calculi studied by us.

Cite as

Bruno C. d. S. Oliveira, Cui Shaobo, and Baber Rehman. The Duality of Subtyping. In 34th European Conference on Object-Oriented Programming (ECOOP 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 166, pp. 29:1-29:29, Schloss Dagstuhl - Leibniz-Zentrum für Informatik (2020)


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@InProceedings{oliveira_et_al:LIPIcs.ECOOP.2020.29,
  author =	{Oliveira, Bruno C. d. S. and Shaobo, Cui and Rehman, Baber},
  title =	{{The Duality of Subtyping}},
  booktitle =	{34th European Conference on Object-Oriented Programming (ECOOP 2020)},
  pages =	{29:1--29:29},
  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.dagstuhl.de/entities/document/10.4230/LIPIcs.ECOOP.2020.29},
  URN =		{urn:nbn:de:0030-drops-131864},
  doi =		{10.4230/LIPIcs.ECOOP.2020.29},
  annote =	{Keywords: DuoTyping, OOP, Duality, Subtyping, Supertyping}
}
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