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Documents authored by Oliveira, Bruno C. d. S.

Document
DOI: 10.4230/LIPIcs.ECOOP.2023.34
Dependent Merges and First-Class Environments

Authors: Jinhao Tan and Bruno C. d. S. Oliveira

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

Abstract
In most programming languages a (runtime) environment stores all the definitions that are available to programmers. Typically, environments are a meta-level notion, used only conceptually or internally in the implementation of programming languages. Only a few programming languages allow environments to be first-class values, which can be manipulated directly in programs. Although there is some research on calculi with first-class environments for statically typed programming languages, these calculi typically have significant restrictions. In this paper we propose a statically typed calculus, called 𝖤_i, with first-class environments. The main novelty of the 𝖤_i calculus is its support for first-class environments, together with an expressive set of operators that manipulate them. Such operators include: reification of the current environment, environment concatenation, environment restriction, and reflection mechanisms for running computations under a given environment. In 𝖤_i any type can act as a context (i.e. an environment type) and contexts are simply types. Furthermore, because 𝖤_i supports subtyping, there is a natural notion of context subtyping. There are two important ideas in 𝖤_i that generalize and are inspired by existing notions in the literature. The 𝖤_i calculus borrows disjoint intersection types and a merge operator, used in 𝖤_i to model contexts and environments, from the λ_i calculus. However, unlike the merges in λ_i, the merges in 𝖤_i can depend on previous components of a merge. From implicit calculi, the 𝖤_i calculus borrows the notion of a query, which allows type-based lookups on environments. In particular, queries are key to the ability of 𝖤_i to reify the current environment, or some parts of it. We prove the determinism and type soundness of 𝖤_i, and show that 𝖤_i can encode all well-typed λ_i programs.
Cite as

Jinhao Tan and Bruno C. d. S. Oliveira. Dependent Merges and First-Class Environments. In 37th European Conference on Object-Oriented Programming (ECOOP 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 263, pp. 34:1-34:32, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)

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@InProceedings{tan_et_al:LIPIcs.ECOOP.2023.34,
  author =	{Tan, Jinhao and Oliveira, Bruno C. d. S.},
  title =	{{Dependent Merges and First-Class Environments}},
  booktitle =	{37th European Conference on Object-Oriented Programming (ECOOP 2023)},
  pages =	{34:1--34:32},
  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.dagstuhl.de/entities/document/10.4230/LIPIcs.ECOOP.2023.34},
  URN =		{urn:nbn:de:0030-drops-182277},
  doi =		{10.4230/LIPIcs.ECOOP.2023.34},
  annote =	{Keywords: First-class Environments, Disjointness, Intersection Types}
}
Document
Artifact
DOI: 10.4230/DARTS.9.2.2
Dependent Merges and First-Class Environments (Artifact)

Authors: Jinhao Tan and Bruno C. d. S. Oliveira

Published in: DARTS, Volume 9, Issue 2, Special Issue of the 37th European Conference on Object-Oriented Programming (ECOOP 2023)

Abstract
This artifact contains the mechanical formalization of the calculi associated with the paper Dependent Merges and First-Class Environments. All of the metatheory has been formalized in Coq theorem prover. The paper studies a statically typed calculus, called 𝖤_i, with first-class environments. The main novelty of the 𝖤_i calculus is its support for first-class environments, together with an expressive set of operators that manipulate them.
Cite as

Jinhao Tan and Bruno C. d. S. Oliveira. Dependent Merges and First-Class Environments (Artifact). In Special Issue of the 37th European Conference on Object-Oriented Programming (ECOOP 2023). Dagstuhl Artifacts Series (DARTS), Volume 9, Issue 2, pp. 2:1-2:3, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)

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@Article{tan_et_al:DARTS.9.2.2,
  author =	{Tan, Jinhao and Oliveira, Bruno C. d. S.},
  title =	{{Dependent Merges and First-Class Environments (Artifact)}},
  pages =	{2:1--2:3},
  journal =	{Dagstuhl Artifacts Series},
  ISSN =	{2509-8195},
  year =	{2023},
  volume =	{9},
  number =	{2},
  editor =	{Tan, Jinhao 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.9.2.2},
  URN =		{urn:nbn:de:0030-drops-182427},
  doi =		{10.4230/DARTS.9.2.2},
  annote =	{Keywords: First-class Environments, Disjointness, Intersection Types}
}
Document
Artifact
DOI: 10.4230/DARTS.8.2.4
Direct Foundations for Compositional Programming (Artifact)

Authors: Andong Fan, Xuejing Huang, Han Xu, Yaozhu Sun, 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
Our companion paper proposes a new formulation of the 𝖥_{i}^{+} calculus with disjoint polymorphism and a merge operator based on Type-Directed Operational Semantics. The artifact contains Coq formalization of the 𝖥_{i}^{+} calculus and our new implementation of the CP language, which demonstrates the new 𝖥_{i}^{+} can serve as the direct foundation for Compositional Programming.
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Andong Fan, Xuejing Huang, Han Xu, Yaozhu Sun, and Bruno C. d. S. Oliveira. Direct Foundations for Compositional Programming (Artifact). In Special Issue of the 36th European Conference on Object-Oriented Programming (ECOOP 2022). Dagstuhl Artifacts Series (DARTS), Volume 8, Issue 2, pp. 4:1-4:3, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)

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@Article{fan_et_al:DARTS.8.2.4,
  author =	{Fan, Andong and Huang, Xuejing and Xu, Han and Sun, Yaozhu and Oliveira, Bruno C. d. S.},
  title =	{{Direct Foundations for Compositional Programming (Artifact)}},
  pages =	{4:1--4:3},
  journal =	{Dagstuhl Artifacts Series},
  ISSN =	{2509-8195},
  year =	{2022},
  volume =	{8},
  number =	{2},
  editor =	{Fan, Andong and Huang, Xuejing and Xu, Han and Sun, Yaozhu 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.8.2.4},
  URN =		{urn:nbn:de:0030-drops-162020},
  doi =		{10.4230/DARTS.8.2.4},
  annote =	{Keywords: Intersection types, disjoint polymorphism, operational semantics}
}
Document
Artifact
DOI: 10.4230/DARTS.8.2.5
Elementary Type Inference (Artifact)

Authors: Jinxu Zhao 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 Appendix of the paper, proofs of theorems declared in the paper, and a sample implementation of the type inference algorithm. The proof contains 3 main results: soundness, completness and decidability of the type-inference algorithm. Moreover, there are several proofs about the declarative system and also a soundness/completeness proof between stable subtyping and a syntax-directed specification.
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Jinxu Zhao and Bruno C. d. S. Oliveira. Elementary Type Inference (Artifact). In Special Issue of the 36th European Conference on Object-Oriented Programming (ECOOP 2022). Dagstuhl Artifacts Series (DARTS), Volume 8, Issue 2, pp. 5:1-5:2, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)

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@Article{zhao_et_al:DARTS.8.2.5,
  author =	{Zhao, Jinxu and Oliveira, Bruno C. d. S.},
  title =	{{Elementary Type Inference (Artifact)}},
  pages =	{5:1--5:2},
  journal =	{Dagstuhl Artifacts Series},
  ISSN =	{2509-8195},
  year =	{2022},
  volume =	{8},
  number =	{2},
  editor =	{Zhao, Jinxu 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.8.2.5},
  URN =		{urn:nbn:de:0030-drops-162036},
  doi =		{10.4230/DARTS.8.2.5},
  annote =	{Keywords: Type Inference}
}
Document
Artifact
DOI: 10.4230/DARTS.8.2.17
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
DOI: 10.4230/LIPIcs.ECOOP.2022.2
Elementary Type Inference

Authors: Jinxu Zhao and Bruno C. d. S. Oliveira

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

Abstract
Languages with polymorphic type systems are made convenient to use by employing type inference to avoid redundant type information. Unfortunately, features such as impredicative types and subtyping make complete type inference very challenging or impossible to realize. This paper presents a form of partial type inference called elementary type inference. Elementary type inference adopts the idea of inferring only monotypes from past work on predicative higher-ranked polymorphism. This idea is extended with the addition of explicit type applications that work for any polytypes. Thus easy (predicative) instantiations can be inferred, while all other (impredicative) instantiations are always possible with explicit type applications without any compromise in expressiveness. Our target is a System F extension with top and bottom types, similar to the language employed by Pierce and Turner in their seminal work on local type inference. We show a sound, complete and decidable type system for a calculus called F_{< :}^e, that targets that extension of System F. A key design choice in F_{< :}^e is to consider top and bottom types as polytypes only. An important technical challenge is that the combination of predicative implicit instantiation and impredicative explicit type applications, in the presence of standard subtyping rules, is non-trivial. Without some restrictions, key properties, such as subsumption and stability of type substitution lemmas, break. To address this problem we introduce a variant of polymorphic subtyping called stable subtyping with some mild restrictions on implicit instantiation. All the results are mechanically formalized in the Abella theorem prover.
Cite as

Jinxu Zhao and Bruno C. d. S. Oliveira. Elementary Type Inference. In 36th European Conference on Object-Oriented Programming (ECOOP 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 222, pp. 2:1-2:28, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)

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@InProceedings{zhao_et_al:LIPIcs.ECOOP.2022.2,
  author =	{Zhao, Jinxu and Oliveira, Bruno C. d. S.},
  title =	{{Elementary Type Inference}},
  booktitle =	{36th European Conference on Object-Oriented Programming (ECOOP 2022)},
  pages =	{2:1--2:28},
  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.2022.2},
  URN =		{urn:nbn:de:0030-drops-162303},
  doi =		{10.4230/LIPIcs.ECOOP.2022.2},
  annote =	{Keywords: Type Inference}
}
Document
DOI: 10.4230/LIPIcs.ECOOP.2022.18
Direct Foundations for Compositional Programming

Authors: Andong Fan, Xuejing Huang, Han Xu, Yaozhu Sun, and Bruno C. d. S. Oliveira

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

Abstract
The recently proposed CP language adopts Compositional Programming: a new modular programming style that solves challenging problems such as the Expression Problem. CP is implemented on top of a polymorphic core language with disjoint intersection types called 𝖥_{i}^{+}. The semantics of 𝖥_{i}^{+} employs an elaboration to a target language and relies on a sophisticated proof technique to prove the coherence of the elaboration. Unfortunately, the proof technique is technically challenging and hard to scale to many common features, including recursion or impredicative polymorphism. Thus, the original formulation of 𝖥_{i}^{+} does not support the two later features, which creates a gap between theory and practice, since CP fundamentally relies on them. This paper presents a new formulation of 𝖥_{i}^{+} based on a type-directed operational semantics (TDOS). The TDOS approach was recently proposed to model the semantics of languages with disjoint intersection types (but without polymorphism). Our work shows that the TDOS approach can be extended to languages with disjoint polymorphism and model the full 𝖥_{i}^{+} calculus. Unlike the elaboration semantics, which gives the semantics to 𝖥_{i}^{+} indirectly via a target language, the TDOS approach gives a semantics to 𝖥_{i}^{+} directly. With a TDOS, there is no need for a coherence proof. Instead, we can simply prove that the semantics is deterministic. The proof of determinism only uses simple reasoning techniques, such as straightforward induction, and is able to handle problematic features such as recursion and impredicative polymorphism. This removes the gap between theory and practice and validates the original proofs of correctness for CP. We formalized the TDOS variant of the 𝖥_{i}^{+} calculus and all its proofs in the Coq proof assistant.
Cite as

Andong Fan, Xuejing Huang, Han Xu, Yaozhu Sun, and Bruno C. d. S. Oliveira. Direct Foundations for Compositional Programming. In 36th European Conference on Object-Oriented Programming (ECOOP 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 222, pp. 18:1-18:28, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)

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@InProceedings{fan_et_al:LIPIcs.ECOOP.2022.18,
  author =	{Fan, Andong and Huang, Xuejing and Xu, Han and Sun, Yaozhu and Oliveira, Bruno C. d. S.},
  title =	{{Direct Foundations for Compositional Programming}},
  booktitle =	{36th European Conference on Object-Oriented Programming (ECOOP 2022)},
  pages =	{18:1--18:28},
  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.2022.18},
  URN =		{urn:nbn:de:0030-drops-162463},
  doi =		{10.4230/LIPIcs.ECOOP.2022.18},
  annote =	{Keywords: Intersection types, disjoint polymorphism, operational semantics}
}
Document
DOI: 10.4230/LIPIcs.ECOOP.2022.25
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
DOI: 10.4230/DARTS.7.2.9
Type-Directed Operational Semantics for Gradual Typing (Artifact)

Authors: Wenjia Ye, Bruno C. d. S. Oliveira, and Xuejing Huang

Published in: DARTS, Volume 7, Issue 2, Special Issue of the 35th European Conference on Object-Oriented Programming (ECOOP 2021)

Abstract
This artifact includes the Coq formalization associated with the paper Type-Directed Operational Semantics for Gradual Typing submitted in ECOOP 2021. The paper illustrates how to employ TDOS on gradually typed languages using two calculi. The first calculus, called λB, is inspired by the semantics of the blame calculus(λB^g) and is sound with λB^g. The second calculus, called λB^r, explores a different design space in the semantics of gradually typed languages. 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 7 explains how to get the docker image for the artifact. Section 8 explains the prerequisites and the steps to run coq files from scratch. Section 9 explains coq files briefly. Section 10 shows the correspondence of important lemmas, definitions and pictures discussed in the paper with their respective Coq formalization.
Cite as

Wenjia Ye, Bruno C. d. S. Oliveira, and Xuejing Huang. Type-Directed Operational Semantics for Gradual Typing (Artifact). In Special Issue of the 35th European Conference on Object-Oriented Programming (ECOOP 2021). Dagstuhl Artifacts Series (DARTS), Volume 7, Issue 2, pp. 9:1-9:6, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)

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@Article{ye_et_al:DARTS.7.2.9,
  author =	{Ye, Wenjia and Oliveira, Bruno C. d. S. and Huang, Xuejing},
  title =	{{Type-Directed Operational Semantics for Gradual Typing (Artifact)}},
  pages =	{9:1--9:6},
  journal =	{Dagstuhl Artifacts Series},
  ISSN =	{2509-8195},
  year =	{2021},
  volume =	{7},
  number =	{2},
  editor =	{Ye, Wenjia and Oliveira, Bruno C. d. S. and Huang, Xuejing},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/DARTS.7.2.9},
  URN =		{urn:nbn:de:0030-drops-140337},
  doi =		{10.4230/DARTS.7.2.9},
  annote =	{Keywords: Gradual Typing, Operational Semantics, Type Systems}
}
Document
Artifact
DOI: 10.4230/DARTS.7.2.11
Compositional Programming (Artifact)

Authors: Weixin Zhang, Yaozhu Sun, and Bruno C. d. S. Oliveira

Published in: DARTS, Volume 7, Issue 2, Special Issue of the 35th European Conference on Object-Oriented Programming (ECOOP 2021)

Abstract
Our main paper presents CP, a Compositional Programming language in a statically typed modular programming style. This artifact includes its Haskell implementation, together with several examples and three case studies written in CP. All code snippets in our main paper can be type-checked and run using our CP interpreter.
Cite as

Weixin Zhang, Yaozhu Sun, and Bruno C. d. S. Oliveira. Compositional Programming (Artifact). In Special Issue of the 35th European Conference on Object-Oriented Programming (ECOOP 2021). Dagstuhl Artifacts Series (DARTS), Volume 7, Issue 2, pp. 11:1-11:2, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)

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@Article{zhang_et_al:DARTS.7.2.11,
  author =	{Zhang, Weixin and Sun, Yaozhu and Oliveira, Bruno C. d. S.},
  title =	{{Compositional Programming (Artifact)}},
  pages =	{11:1--11:2},
  journal =	{Dagstuhl Artifacts Series},
  ISSN =	{2509-8195},
  year =	{2021},
  volume =	{7},
  number =	{2},
  editor =	{Zhang, Weixin and Sun, Yaozhu 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.7.2.11},
  URN =		{urn:nbn:de:0030-drops-140356},
  doi =		{10.4230/DARTS.7.2.11},
  annote =	{Keywords: Expression Problem, Compositionality, Traits}
}
Document
DOI: 10.4230/LIPIcs.ECOOP.2021.12
Type-Directed Operational Semantics for Gradual Typing

Authors: Wenjia Ye, Bruno C. d. S. Oliveira, and Xuejing Huang

Published in: LIPIcs, Volume 194, 35th European Conference on Object-Oriented Programming (ECOOP 2021)

Abstract
The semantics of gradually typed languages is typically given indirectly via an elaboration into a cast calculus. This contrasts with more conventional formulations of programming language semantics, where the semantics of a language is given directly using, for instance, an operational semantics. This paper presents a new approach to give the semantics of gradually typed languages directly. We use a recently proposed variant of small-step operational semantics called type-directed operational semantics (TDOS). In TDOS type annotations become operationally relevant and can affect the result of a program. In the context of a gradually typed language, such type annotations are used to trigger type-based conversions on values. We illustrate how to employ TDOS on gradually typed languages using two calculi. The first calculus, called λ B^g, is inspired by the semantics of the blame calculus, but it has implicit type conversions, enabling it to be used as a gradually typed language. The second calculus, called λ B^r, explores a different design space in the semantics of gradually typed languages. It uses a so-called blame recovery semantics, which enables eliminating some false positives where blame is raised but normal computation could succeed. For both calculi, type safety is proved. Furthermore we show that the semantics of λ B^g is sound with respect to the semantics of the blame calculus, and that λ B^r comes with a gradual guarantee. All the results have been mechanically formalized in the Coq theorem prover.
Cite as

Wenjia Ye, Bruno C. d. S. Oliveira, and Xuejing Huang. Type-Directed Operational Semantics for Gradual Typing. In 35th European Conference on Object-Oriented Programming (ECOOP 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 194, pp. 12:1-12:30, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)

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@InProceedings{ye_et_al:LIPIcs.ECOOP.2021.12,
  author =	{Ye, Wenjia and Oliveira, Bruno C. d. S. and Huang, Xuejing},
  title =	{{Type-Directed Operational Semantics for Gradual Typing}},
  booktitle =	{35th European Conference on Object-Oriented Programming (ECOOP 2021)},
  pages =	{12:1--12:30},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-190-0},
  ISSN =	{1868-8969},
  year =	{2021},
  volume =	{194},
  editor =	{M{\o}ller, Anders and Sridharan, Manu},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ECOOP.2021.12},
  URN =		{urn:nbn:de:0030-drops-140551},
  doi =		{10.4230/LIPIcs.ECOOP.2021.12},
  annote =	{Keywords: Gradual Typing, Type Systems, Operational Semantics}
}
Document
Artifact
DOI: 10.4230/DARTS.6.2.8
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
Artifact
DOI: 10.4230/DARTS.6.2.9
A Type-Directed Operational Semantics For a Calculus with a Merge Operator (Artifact)

Authors: Xuejing Huang and Bruno C. d. S. Oliveira

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

Abstract
Our companion paper proposes a type-directed operational semantics (TDOS) for λ_i^{:}: a calculus with intersection types and a merge operator. The artifact contains the specification of λ_i^{:} and its TDOS, and related Coq code. λ_i^{:} is formalized using the locally nameless representation with cofinite quantification. The Coq definition and some infrastructure code are generated by Ott and LNgen. λ_i^{:} is inspired by two closely related calculi by Dunfield (2014) and Oliveira et al. (2016), and a simple variant of it is designed to demonstrate the possibility to match with them without any modification. To relate the two calculi with λ_i^{:}, a sound theorem on semantics and a completeness theorem on typing are proved for each variant. In addition, we extended the bidirectional typing of Oliveira et al.’s λ_i calculus, and designed an elaboration from it to λ_i^{:}, to show that many of λ_i^{:}’s explicit annotations can be inferred automatically.
Cite as

Xuejing Huang and Bruno C. d. S. Oliveira. A Type-Directed Operational Semantics For a Calculus with a Merge Operator (Artifact). In Special Issue of the 34th European Conference on Object-Oriented Programming (ECOOP 2020). Dagstuhl Artifacts Series (DARTS), Volume 6, Issue 2, pp. 9:1-9:4, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

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@Article{huang_et_al:DARTS.6.2.9,
  author =	{Huang, Xuejing and Oliveira, Bruno C. d. S.},
  title =	{{A Type-Directed Operational Semantics For a Calculus with a Merge Operator (Artifact)}},
  pages =	{9:1--9:4},
  journal =	{Dagstuhl Artifacts Series},
  ISSN =	{2509-8195},
  year =	{2020},
  volume =	{6},
  number =	{2},
  editor =	{Huang, Xuejing 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.6.2.9},
  URN =		{urn:nbn:de:0030-drops-132060},
  doi =		{10.4230/DARTS.6.2.9},
  annote =	{Keywords: operational semantics, type systems, intersection types}
}
Document
DOI: 10.4230/LIPIcs.ECOOP.2020.26
A Type-Directed Operational Semantics For a Calculus with a Merge Operator

Authors: Xuejing Huang and Bruno C. d. S. Oliveira

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

Abstract
Calculi with disjoint intersection types and a merge operator provide general mechanisms that can subsume various other features. Such calculi can also encode highly dynamic forms of object composition, which capture common programming patterns in dynamically typed languages (such as JavaScript) in a fully statically typed manner. Unfortunately, unlike many other foundational calculi (such as System F, System F_{< :} or Featherweight Java), recent calculi with the merge operator lack a (direct) operational semantics with standard and expected properties such as determinism and subject-reduction. Furthermore the metatheory for such calculi can only account for terminating programs, which is a significant restriction in practice. This paper proposes a type-directed operational semantics (TDOS) for λ_i^{:}: a calculus with intersection types and a merge operator. The calculus is inspired by two closely related calculi by Dunfield (2014) and Oliveira et al. (2016). Although Dunfield proposes a direct small-step semantics for her calculus, her semantics lacks both determinism and subject-reduction. Using our TDOS we obtain a direct semantics for λ_i^{:} that has both properties. To fully obtain determinism, the λ_i^{:} calculus employs a disjointness restriction proposed in Oliveira et al.’s λ_i calculus. As an added benefit the TDOS approach deals with recursion in a straightforward way, unlike λ_i and subsequent calculi where recursion is problematic. To further relate λ_i^{:} to the calculi by Dunfield and Oliveira et al. we show two results. Firstly, the semantics of λ_i^{:} is sound with respect to Dunfield’s small-step semantics. Secondly, we show that the type system of λ_i^{:} is complete with respect to the λ_i type system. All results have been fully formalized in the Coq theorem prover.
Cite as

Xuejing Huang and Bruno C. d. S. Oliveira. A Type-Directed Operational Semantics For a Calculus with a Merge Operator. In 34th European Conference on Object-Oriented Programming (ECOOP 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 166, pp. 26:1-26:32, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

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@InProceedings{huang_et_al:LIPIcs.ECOOP.2020.26,
  author =	{Huang, Xuejing and Oliveira, Bruno C. d. S.},
  title =	{{A Type-Directed Operational Semantics For a Calculus with a Merge Operator}},
  booktitle =	{34th European Conference on Object-Oriented Programming (ECOOP 2020)},
  pages =	{26:1--26:32},
  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.2020.26},
  URN =		{urn:nbn:de:0030-drops-131832},
  doi =		{10.4230/LIPIcs.ECOOP.2020.26},
  annote =	{Keywords: operational semantics, type systems, intersection types}
}
Document
DOI: 10.4230/LIPIcs.ECOOP.2020.27
Row and Bounded Polymorphism via Disjoint Polymorphism

Authors: Ningning Xie, Bruno C. d. S. Oliveira, Xuan Bi, and Tom Schrijvers

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

Abstract
Polymorphism and subtyping are important features in mainstream OO languages. The most common way to integrate the two is via 𝖥_{< :} style bounded quantification. A closely related mechanism is row polymorphism, which provides an alternative to subtyping, while still enabling many of the same applications. Yet another approach is to have type systems with intersection types and polymorphism. A recent addition to this design space are calculi with disjoint intersection types and disjoint polymorphism. With all these alternatives it is natural to wonder how they are related. This paper provides an answer to this question. We show that disjoint polymorphism can recover forms of both row polymorphism and bounded polymorphism, while retaining key desirable properties, such as type-safety and decidability. Furthermore, we identify the extra power of disjoint polymorphism which enables additional features that cannot be easily encoded in calculi with row polymorphism or bounded quantification alone. Ultimately we expect that our work is useful to inform language designers about the expressive power of those common features, and to simplify implementations and metatheory of feature-rich languages with polymorphism and subtyping.
Cite as

Ningning Xie, Bruno C. d. S. Oliveira, Xuan Bi, and Tom Schrijvers. Row and Bounded Polymorphism via Disjoint Polymorphism. In 34th European Conference on Object-Oriented Programming (ECOOP 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 166, pp. 27:1-27:30, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

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@InProceedings{xie_et_al:LIPIcs.ECOOP.2020.27,
  author =	{Xie, Ningning and Oliveira, Bruno C. d. S. and Bi, Xuan and Schrijvers, Tom},
  title =	{{Row and Bounded Polymorphism via Disjoint Polymorphism}},
  booktitle =	{34th European Conference on Object-Oriented Programming (ECOOP 2020)},
  pages =	{27:1--27:30},
  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.2020.27},
  URN =		{urn:nbn:de:0030-drops-131846},
  doi =		{10.4230/LIPIcs.ECOOP.2020.27},
  annote =	{Keywords: Intersection types, bounded polymorphism, row polymorphism}
}
Document
DOI: 10.4230/LIPIcs.ECOOP.2020.29
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}
}
Document
DOI: 10.4230/LIPIcs.ECOOP.2018.9
Typed First-Class Traits

Authors: Xuan Bi and Bruno C. d. S. Oliveira

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

Abstract
Many dynamically-typed languages (including JavaScript, Ruby, Python or Racket) support first-class classes, or related concepts such as first-class traits and/or mixins. In those languages classes are first-class values and, like any other values, they can be passed as an argument, or returned from a function. Furthermore first-class classes support dynamic inheritance: i.e. they can inherit from other classes at runtime, enabling programmers to abstract over the inheritance hierarchy. In contrast, type system limitations prevent most statically-typed languages from having first-class classes and dynamic inheritance. This paper shows the design of SEDEL: a polymorphic statically-typed language with first-class traits, supporting dynamic inheritance as well as conventional OO features such as dynamic dispatching and abstract methods. To address the challenges of type-checking first-class traits, SEDEL employs a type system based on the recent work on disjoint intersection types and disjoint polymorphism. The novelty of SEDEL over core disjoint intersection calculi are source level features for practical OO programming, including first-class traits with dynamic inheritance, dynamic dispatching and abstract methods. Inspired by Cook and Palsberg's work on the denotational semantics for inheritance, we show how to design a source language that can be elaborated into Alpuim et al.'s F_{i} (a core polymorphic calculus with records supporting disjoint polymorphism). We illustrate the applicability of SEDEL with several example uses for first-class traits, and a case study that modularizes programming language interpreters using a highly modular form of visitors.
Cite as

Xuan Bi and Bruno C. d. S. Oliveira. Typed First-Class Traits. In 32nd European Conference on Object-Oriented Programming (ECOOP 2018). Leibniz International Proceedings in Informatics (LIPIcs), Volume 109, pp. 9:1-9:28, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)

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@InProceedings{bi_et_al:LIPIcs.ECOOP.2018.9,
  author =	{Bi, Xuan and Oliveira, Bruno C. d. S.},
  title =	{{Typed First-Class Traits}},
  booktitle =	{32nd European Conference on Object-Oriented Programming (ECOOP 2018)},
  pages =	{9:1--9:28},
  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.2018.9},
  URN =		{urn:nbn:de:0030-drops-92145},
  doi =		{10.4230/LIPIcs.ECOOP.2018.9},
  annote =	{Keywords: traits, extensible designs}
}
Document
DOI: 10.4230/LIPIcs.ECOOP.2018.20
FHJ: A Formal Model for Hierarchical Dispatching and Overriding

Authors: Yanlin Wang, Haoyuan Zhang, Bruno C. d. S. Oliveira, and Marco Servetto

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

Abstract
Multiple inheritance is a valuable feature for Object-Oriented Programming. However, it is also tricky to get right, as illustrated by the extensive literature on the topic. A key issue is the ambiguity arising from inheriting multiple parents, which can have conflicting methods. Numerous existing work provides solutions for conflicts which arise from diamond inheritance: i.e. conflicts that arise from implementations sharing a common ancestor. However, most mechanisms are inadequate to deal with unintentional method conflicts: conflicts which arise from two unrelated methods that happen to share the same name and signature. This paper presents a new model called Featherweight Hierarchical Java (FHJ) that deals with unintentional method conflicts. In our new model, which is partly inspired by C++, conflicting methods arising from unrelated methods can coexist in the same class, and hierarchical dispatching supports unambiguous lookups in the presence of such conflicting methods. To avoid ambiguity, hierarchical information is employed in method dispatching, which uses a combination of static and dynamic type information to choose the implementation of a method at run-time. Furthermore, unlike all existing inheritance models, our model supports hierarchical method overriding: that is, methods can be independently overridden along the multiple inheritance hierarchy. We give illustrative examples of our language and features and formalize FHJ as a minimal Featherweight-Java style calculus.
Cite as

Yanlin Wang, Haoyuan Zhang, Bruno C. d. S. Oliveira, and Marco Servetto. FHJ: A Formal Model for Hierarchical Dispatching and Overriding. In 32nd European Conference on Object-Oriented Programming (ECOOP 2018). Leibniz International Proceedings in Informatics (LIPIcs), Volume 109, pp. 20:1-20:30, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)

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@InProceedings{wang_et_al:LIPIcs.ECOOP.2018.20,
  author =	{Wang, Yanlin and Zhang, Haoyuan and Oliveira, Bruno C. d. S. and Servetto, Marco},
  title =	{{FHJ: A Formal Model for Hierarchical Dispatching and Overriding}},
  booktitle =	{32nd European Conference on Object-Oriented Programming (ECOOP 2018)},
  pages =	{20:1--20:30},
  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.2018.20},
  URN =		{urn:nbn:de:0030-drops-92259},
  doi =		{10.4230/LIPIcs.ECOOP.2018.20},
  annote =	{Keywords: multiple inheritance, hierarchical dispatching, OOP, language design}
}
Document
DOI: 10.4230/LIPIcs.ECOOP.2018.22
The Essence of Nested Composition

Authors: Xuan Bi, Bruno C. d. S. Oliveira, and Tom Schrijvers

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

Abstract
Calculi with disjoint intersection types support an introduction form for intersections called the merge operator, while retaining a coherent semantics. Disjoint intersections types have great potential to serve as a foundation for powerful, flexible and yet type-safe and easy to reason OO languages. This paper shows how to significantly increase the expressive power of disjoint intersection types by adding support for nested subtyping and composition, which enables simple forms of family polymorphism to be expressed in the calculus. The extension with nested subtyping and composition is challenging, for two different reasons. Firstly, the subtyping relation that supports these features is non-trivial, especially when it comes to obtaining an algorithmic version. Secondly, the syntactic method used to prove coherence for previous calculi with disjoint intersection types is too inflexible, making it hard to extend those calculi with new features (such as nested subtyping). We show how to address the first problem by adapting and extending the Barendregt, Coppo and Dezani (BCD) subtyping rules for intersections with records and coercions. A sound and complete algorithmic system is obtained by using an approach inspired by Pierce's work. To address the second problem we replace the syntactic method to prove coherence, by a semantic proof method based on logical relations. Our work has been fully formalized in Coq, and we have an implementation of our calculus.
Cite as

Xuan Bi, Bruno C. d. S. Oliveira, and Tom Schrijvers. The Essence of Nested Composition. In 32nd European Conference on Object-Oriented Programming (ECOOP 2018). Leibniz International Proceedings in Informatics (LIPIcs), Volume 109, pp. 22:1-22:33, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)

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@InProceedings{bi_et_al:LIPIcs.ECOOP.2018.22,
  author =	{Bi, Xuan and Oliveira, Bruno C. d. S. and Schrijvers, Tom},
  title =	{{The Essence of Nested Composition}},
  booktitle =	{32nd European Conference on Object-Oriented Programming (ECOOP 2018)},
  pages =	{22:1--22:33},
  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.2018.22},
  URN =		{urn:nbn:de:0030-drops-92275},
  doi =		{10.4230/LIPIcs.ECOOP.2018.22},
  annote =	{Keywords: nested composition, family polymorphism, intersection types, coherence}
}
Document
DOI: 10.4230/DARTS.4.3.5
The Essence of Nested Composition (Artifact)

Authors: Xuan Bi, Bruno C. d. S. Oliveira, and Tom Schrijvers

Published in: DARTS, Volume 4, Issue 3, Special Issue of the 32nd European Conference on Object-Oriented Programming (ECOOP 2018)

Abstract
The artifact contains the Coq formalization of \name, a simple calculus with disjoint intersection types supporting nested subtyping and composition, as described in the companion paper.
Cite as

Xuan Bi, Bruno C. d. S. Oliveira, and Tom Schrijvers. The Essence of Nested Composition (Artifact). In Special Issue of the 32nd European Conference on Object-Oriented Programming (ECOOP 2018). Dagstuhl Artifacts Series (DARTS), Volume 4, Issue 3, pp. 5:1-5:2, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)

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@Article{bi_et_al:DARTS.4.3.5,
  author =	{Bi, Xuan and Oliveira, Bruno C. d. S. and Schrijvers, Tom},
  title =	{{The Essence of Nested Composition (Artifact)}},
  pages =	{5:1--5:2},
  journal =	{Dagstuhl Artifacts Series},
  ISSN =	{2509-8195},
  year =	{2018},
  volume =	{4},
  number =	{3},
  editor =	{Bi, Xuan and Oliveira, Bruno C. d. S. and Schrijvers, Tom},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/DARTS.4.3.5},
  URN =		{urn:nbn:de:0030-drops-92363},
  doi =		{10.4230/DARTS.4.3.5},
  annote =	{Keywords: nested composition, family polymorphism, intersection types, coherence}
}
Document
DOI: 10.4230/DARTS.4.3.9
Typed First-Class Traits (Artifact)

Authors: Xuan Bi and Bruno C. d. S. Oliveira

Published in: DARTS, Volume 4, Issue 3, Special Issue of the 32nd European Conference on Object-Oriented Programming (ECOOP 2018)

Abstract
This artifact contains the prototype Haskell implementation of SEDEL, with support for first-class traits, as described in the companion paper. This artifact also contains the source code of the case study on "Anatomy of Programming Languages", illustrating how effective SEDEL is in terms of modularizing programming language features. For comparison, it also includes a vanilla Haskell implementation of the case study without any code reuse.
Cite as

Xuan Bi and Bruno C. d. S. Oliveira. Typed First-Class Traits (Artifact). In Special Issue of the 32nd European Conference on Object-Oriented Programming (ECOOP 2018). Dagstuhl Artifacts Series (DARTS), Volume 4, Issue 3, pp. 9:1-9:2, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)

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@Article{bi_et_al:DARTS.4.3.9,
  author =	{Bi, Xuan and Oliveira, Bruno C. d. S.},
  title =	{{Typed First-Class Traits (Artifact)}},
  pages =	{9:1--9:2},
  journal =	{Dagstuhl Artifacts Series},
  ISSN =	{2509-8195},
  year =	{2018},
  volume =	{4},
  number =	{3},
  editor =	{Bi, Xuan 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.4.3.9},
  URN =		{urn:nbn:de:0030-drops-92407},
  doi =		{10.4230/DARTS.4.3.9},
  annote =	{Keywords: traits, extensible designs}
}
Document
DOI: 10.4230/DARTS.3.2.10
EVF: An Extensible and Expressive Visitor Framework for Programming Language Reuse (Artifact)

Authors: Weixin Zhang and Bruno C. d. S. Oliveira

Published in: DARTS, Volume 3, Issue 2, Special Issue of the 31st European Conference on Object-Oriented Programming (ECOOP 2017)

Abstract
This artifact is based on EVF, an extensible and expressive Java visitor framework. EVF aims at reducing the effort involved in creation and reuse of programming languages. EVF an annotation processor that automatically generate boilerplate ASTs and AST for a given an Object Algebra interface. This artifact contains source code of the case study on "Types and Programming Languages", illustrating how effective EVF is in modularizing programming languages. There is also a microbenchmark in the artifact that shows that EVF has reasonable performance with respect to traditional visitors.
Cite as

Weixin Zhang and Bruno C. d. S. Oliveira. EVF: An Extensible and Expressive Visitor Framework for Programming Language Reuse (Artifact). In Special Issue of the 31st European Conference on Object-Oriented Programming (ECOOP 2017). Dagstuhl Artifacts Series (DARTS), Volume 3, Issue 2, pp. 10:1-10:2, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2017)

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@Article{zhang_et_al:DARTS.3.2.10,
  author =	{Zhang, Weixin and Oliveira, Bruno C. d. S.},
  title =	{{EVF: An Extensible and Expressive Visitor Framework for Programming Language Reuse (Artifact)}},
  pages =	{10:1--10:2},
  journal =	{Dagstuhl Artifacts Series},
  ISSN =	{2509-8195},
  year =	{2017},
  volume =	{3},
  number =	{2},
  editor =	{Zhang, Weixin 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.3.2.10},
  URN =		{urn:nbn:de:0030-drops-72918},
  doi =		{10.4230/DARTS.3.2.10},
  annote =	{Keywords: visitor pattern, object algebras, modularity, domain-specific languages}
}
Document
DOI: 10.4230/LIPIcs.ECOOP.2017.29
EVF: An Extensible and Expressive Visitor Framework for Programming Language Reuse

Authors: Weixin Zhang and Bruno C. d. S. Oliveira

Published in: LIPIcs, Volume 74, 31st European Conference on Object-Oriented Programming (ECOOP 2017)

Abstract
Object Algebras are a design pattern that enables extensibility, modularity, and reuse in mainstream object-oriented languages such as Java. The theoretical foundations of Object Algebras are rooted on Church encodings of datatypes, which are in turn closely related to folds in functional programming. Unfortunately, it is well-known that certain programs are difficult to write, and may incur performance penalties when using Church-encodings/folds. This paper presents EVF: an extensible and expressive Java Visitor framework. The visitors supported by EVF generalize Object Algebras and enable writing programs using a generally recursive style rather than folds. The use of such generally recursive style enables users to more naturally write programs, which would otherwise require contrived workarounds using a fold-like structure. EVF visitors retain the type-safe extensibility of Object Algebras. The key advance in EVF is a novel technique to support extensible external visitors. Extensible external visitors are able to control traversals with direct access to the data structure being traversed, allowing dependent operations to be defined modularly without the need of advanced type system features. To make EVF practical, the framework employs annotations to automatically generate large amounts of boilerplate code related to visitors and traversals. To illustrate the applicability of EVF we conduct a case study, which refactors a large number of non-modular interpreters from the “Types and Programming Languages” (TAPL) book. Using EVF we are able to create a modular software product line (SPL) of the TAPL interpreters, enabling sharing of large portions of code and features. The TAPL software product line contains several modular operations, which would be non-trivial to define with standard Object Algebras.
Cite as

Weixin Zhang and Bruno C. d. S. Oliveira. EVF: An Extensible and Expressive Visitor Framework for Programming Language Reuse. In 31st European Conference on Object-Oriented Programming (ECOOP 2017). Leibniz International Proceedings in Informatics (LIPIcs), Volume 74, pp. 29:1-29:32, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2017)

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@InProceedings{zhang_et_al:LIPIcs.ECOOP.2017.29,
  author =	{Zhang, Weixin and Oliveira, Bruno C. d. S.},
  title =	{{EVF: An Extensible and Expressive Visitor Framework for Programming Language Reuse}},
  booktitle =	{31st European Conference on Object-Oriented Programming (ECOOP 2017)},
  pages =	{29:1--29:32},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-035-4},
  ISSN =	{1868-8969},
  year =	{2017},
  volume =	{74},
  editor =	{M\"{u}ller, Peter},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ECOOP.2017.29},
  URN =		{urn:nbn:de:0030-drops-72749},
  doi =		{10.4230/LIPIcs.ECOOP.2017.29},
  annote =	{Keywords: Visitor Pattern, Object Algebras, Modularity, Domain-Specific Languages}
}
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