DROPS

Volume

LIPIcs, Volume 166

34th European Conference on Object-Oriented Programming (ECOOP 2020)

ECOOP 2020, November 15-17, 2020, Berlin, Germany (Virtual Conference)

Editors: Robert Hirschfeld and Tobias Pape

Document

Complete Volume

DOI: 10.4230/LIPIcs.ECOOP.2020

LIPIcs, Volume 166, ECOOP 2020, Complete Volume

Authors: Robert Hirschfeld and Tobias Pape

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

Abstract

LIPIcs, Volume 166, ECOOP 2020, Complete Volume

Cite as

34th European Conference on Object-Oriented Programming (ECOOP 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 166, pp. 1-906, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

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@Proceedings{hirschfeld_et_al:LIPIcs.ECOOP.2020,
  title =	{{LIPIcs, Volume 166, ECOOP 2020, Complete Volume}},
  booktitle =	{34th European Conference on Object-Oriented Programming (ECOOP 2020)},
  pages =	{1--906},
  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},
  URN =		{urn:nbn:de:0030-drops-131566},
  doi =		{10.4230/LIPIcs.ECOOP.2020},
  annote =	{Keywords: LIPIcs, Volume 166, ECOOP 2020, Complete Volume}
}

Document

Front Matter

DOI: 10.4230/LIPIcs.ECOOP.2020.0

Front Matter, Table of Contents, Preface, Conference Organization

Authors: Robert Hirschfeld and Tobias Pape

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

Abstract

Front Matter, Table of Contents, Preface, Conference Organization

Cite as

34th European Conference on Object-Oriented Programming (ECOOP 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 166, pp. 0:i-0:xxviii, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

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@InProceedings{hirschfeld_et_al:LIPIcs.ECOOP.2020.0,
  author =	{Hirschfeld, Robert and Pape, Tobias},
  title =	{{Front Matter, Table of Contents, Preface, Conference Organization}},
  booktitle =	{34th European Conference on Object-Oriented Programming (ECOOP 2020)},
  pages =	{0:i--0:xxviii},
  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.2020.0},
  URN =		{urn:nbn:de:0030-drops-131572},
  doi =		{10.4230/LIPIcs.ECOOP.2020.0},
  annote =	{Keywords: Front Matter, Table of Contents, Preface, Conference Organization}
}

Document

DOI: 10.4230/LIPIcs.ECOOP.2020.1

Sound Regular Corecursion in coFJ

Authors: Davide Ancona, Pietro Barbieri, Francesco Dagnino, and Elena Zucca

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

Abstract

The aim of the paper is to provide solid foundations for a programming paradigm natively supporting the creation and manipulation of cyclic data structures. To this end, we describe coFJ, a Java-like calculus where objects can be infinite and methods are equipped with a codefinition (an alternative body). We provide an abstract semantics of the calculus based on the framework of inference systems with corules. In coFJ with this semantics, FJ recursive methods on finite objects can be extended to infinite objects as well, and behave as desired by the programmer, by specifying a codefinition. We also describe an operational semantics which can be directly implemented in a programming language, and prove the soundness of such semantics with respect to the abstract one.

Cite as

Davide Ancona, Pietro Barbieri, Francesco Dagnino, and Elena Zucca. Sound Regular Corecursion in coFJ. In 34th European Conference on Object-Oriented Programming (ECOOP 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 166, pp. 1:1-1:28, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

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@InProceedings{ancona_et_al:LIPIcs.ECOOP.2020.1,
  author =	{Ancona, Davide and Barbieri, Pietro and Dagnino, Francesco and Zucca, Elena},
  title =	{{Sound Regular Corecursion in coFJ}},
  booktitle =	{34th European Conference on Object-Oriented Programming (ECOOP 2020)},
  pages =	{1:1--1:28},
  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.2020.1},
  URN =		{urn:nbn:de:0030-drops-131582},
  doi =		{10.4230/LIPIcs.ECOOP.2020.1},
  annote =	{Keywords: Operational semantics, coinduction, programming paradigms, regular terms}
}

Document

DOI: 10.4230/LIPIcs.ECOOP.2020.2

Perfect Is the Enemy of Good: Best-Effort Program Synthesis

Authors: Hila Peleg and Nadia Polikarpova

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

Abstract

Program synthesis promises to help software developers with everyday tasks by generating code snippets automatically from input-output examples and other high-level specifications. The conventional wisdom is that a synthesizer must always satisfy the specification exactly. We conjecture that this all-or-nothing paradigm stands in the way of adopting program synthesis as a developer tool: in practice, the user-written specification often contains errors or is simply too hard for the synthesizer to solve within a reasonable time; in these cases, the user is left with a single over-fitted result or, more often than not, no result at all. In this paper we propose a new program synthesis paradigm we call best-effort program synthesis, where the synthesizer returns a ranked list of partially-valid results, i.e. programs that satisfy some part of the specification. To support this paradigm, we develop best-effort enumeration, a new synthesis algorithm that extends a popular program enumeration technique with the ability to accumulate and return multiple partially-valid results with minimal overhead. We implement this algorithm in a tool called BESTER, and evaluate it on 79 synthesis benchmarks from the literature. Contrary to the conventional wisdom, our evaluation shows that BESTER returns useful results even when the specification is flawed or too hard: i) for all benchmarks with an error in the specification, the top three BESTER results contain the correct solution, and ii) for most hard benchmarks, the top three results contain non-trivial fragments of the correct solution. We also performed an exploratory user study, which confirms our intuition that partially-valid results are useful: the study shows that programmers use the output of the synthesizer for comprehension and often incorporate it into their solutions.

Cite as

Hila Peleg and Nadia Polikarpova. Perfect Is the Enemy of Good: Best-Effort Program Synthesis. In 34th European Conference on Object-Oriented Programming (ECOOP 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 166, pp. 2:1-2:30, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

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@InProceedings{peleg_et_al:LIPIcs.ECOOP.2020.2,
  author =	{Peleg, Hila and Polikarpova, Nadia},
  title =	{{Perfect Is the Enemy of Good: Best-Effort Program Synthesis}},
  booktitle =	{34th European Conference on Object-Oriented Programming (ECOOP 2020)},
  pages =	{2:1--2:30},
  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-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.ECOOP.2020.2},
  URN =		{urn:nbn:de:0030-drops-131593},
  doi =		{10.4230/LIPIcs.ECOOP.2020.2},
  annote =	{Keywords: Program Synthesis, Programming by Example}
}

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.2020.4

Static Race Detection and Mutex Safety and Liveness for Go Programs

Authors: Julia Gabet and Nobuko Yoshida

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

Abstract

Go is a popular concurrent programming language thanks to its ability to efficiently combine concurrency and systems programming. In Go programs, a number of concurrency bugs can be caused by a mixture of data races and communication problems. In this paper, we develop a theory based on behavioural types to statically detect data races and deadlocks in Go programs. We first specify lock safety/liveness and data race properties over a Go program model, using the happens-before relation defined in the Go memory model. We represent these properties of programs in a μ-calculus model of types, and validate them using type-level model-checking. We then extend the framework to account for Go’s channels, and implement a static verification tool which can detect concurrency errors. This is, to the best of our knowledge, the first static verification framework of this kind for the Go language, uniformly analysing concurrency errors caused by a mix of shared memory accesses and asynchronous message-passing communications.

Cite as

Julia Gabet and Nobuko Yoshida. Static Race Detection and Mutex Safety and Liveness for Go Programs. In 34th European Conference on Object-Oriented Programming (ECOOP 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 166, pp. 4:1-4:30, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

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@InProceedings{gabet_et_al:LIPIcs.ECOOP.2020.4,
  author =	{Gabet, Julia and Yoshida, Nobuko},
  title =	{{Static Race Detection and Mutex Safety and Liveness for Go Programs}},
  booktitle =	{34th European Conference on Object-Oriented Programming (ECOOP 2020)},
  pages =	{4:1--4:30},
  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.2020.4},
  URN =		{urn:nbn:de:0030-drops-131615},
  doi =		{10.4230/LIPIcs.ECOOP.2020.4},
  annote =	{Keywords: Go language, behavioural types, race detection, happens-before relation, safety, liveness}
}

Document

DOI: 10.4230/LIPIcs.ECOOP.2020.5

Reconciling Event Structures with Modern Multiprocessors

Authors: Evgenii Moiseenko, Anton Podkopaev, Ori Lahav, Orestis Melkonian, and Viktor Vafeiadis

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

Abstract

Weakestmo is a recently proposed memory consistency model that uses event structures to resolve the infamous "out-of-thin-air" problem and to enable efficient compilation to hardware. Nevertheless, this latter property - compilation correctness - has not yet been formally established. This paper closes this gap by establishing correctness of the intended compilation schemes from Weakestmo to a wide range of formal hardware memory models (x86, POWER, ARMv7, ARMv8) in the Coq proof assistant. Our proof is the first that establishes correctness of compilation of an event-structure-based model that forbids "out-of-thin-air" behaviors, as well as the first mechanized compilation proof of a weak memory model supporting sequentially consistent accesses to such a range of hardware platforms. Our compilation proof goes via the recent Intermediate Memory Model (IMM), which we suitably extend with sequentially consistent accesses.

Cite as

Evgenii Moiseenko, Anton Podkopaev, Ori Lahav, Orestis Melkonian, and Viktor Vafeiadis. Reconciling Event Structures with Modern Multiprocessors. In 34th European Conference on Object-Oriented Programming (ECOOP 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 166, pp. 5:1-5:26, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

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@InProceedings{moiseenko_et_al:LIPIcs.ECOOP.2020.5,
  author =	{Moiseenko, Evgenii and Podkopaev, Anton and Lahav, Ori and Melkonian, Orestis and Vafeiadis, Viktor},
  title =	{{Reconciling Event Structures with Modern Multiprocessors}},
  booktitle =	{34th European Conference on Object-Oriented Programming (ECOOP 2020)},
  pages =	{5:1--5:26},
  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.2020.5},
  URN =		{urn:nbn:de:0030-drops-131622},
  doi =		{10.4230/LIPIcs.ECOOP.2020.5},
  annote =	{Keywords: Weak Memory Consistency, Event Structures, IMM, Weakestmo}
}

Document

DOI: 10.4230/LIPIcs.ECOOP.2020.6

Don't Panic! Better, Fewer, Syntax Errors for LR Parsers

Authors: Lukas Diekmann and Laurence Tratt

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

Abstract

Syntax errors are generally easy to fix for humans, but not for parsers in general nor LR parsers in particular. Traditional "panic mode" error recovery, though easy to implement and applicable to any grammar, often leads to a cascading chain of errors that drown out the original. More advanced error recovery techniques suffer less from this problem but have seen little practical use because their typical performance was seen as poor, their worst case unbounded, and the repairs they reported arbitrary. In this paper we introduce the CPCT+ algorithm, and an implementation of that algorithm, that address these issues. First, CPCT+ reports the complete set of minimum cost repair sequences for a given location, allowing programmers to select the one that best fits their intention. Second, on a corpus of 200,000 real-world syntactically invalid Java programs, CPCT+ is able to repair 98.37%±0.017% of files within a timeout of 0.5s. Finally, CPCT+ uses the complete set of minimum cost repair sequences to reduce the cascading error problem, where incorrect error recovery causes further spurious syntax errors to be identified. Across the test corpus, CPCT+ reports 435,812±473 error locations to the user, reducing the cascading error problem substantially relative to the 981,628±0 error locations reported by panic mode.

Cite as

Lukas Diekmann and Laurence Tratt. Don't Panic! Better, Fewer, Syntax Errors for LR Parsers. In 34th European Conference on Object-Oriented Programming (ECOOP 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 166, pp. 6:1-6:32, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

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@InProceedings{diekmann_et_al:LIPIcs.ECOOP.2020.6,
  author =	{Diekmann, Lukas and Tratt, Laurence},
  title =	{{Don't Panic! Better, Fewer, Syntax Errors for LR Parsers}},
  booktitle =	{34th European Conference on Object-Oriented Programming (ECOOP 2020)},
  pages =	{6:1--6:32},
  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-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.ECOOP.2020.6},
  URN =		{urn:nbn:de:0030-drops-131630},
  doi =		{10.4230/LIPIcs.ECOOP.2020.6},
  annote =	{Keywords: Parsing, error recovery, programming languages}
}

Document

DOI: 10.4230/LIPIcs.ECOOP.2020.7

K-LLVM: A Relatively Complete Semantics of LLVM IR

Authors: Liyi Li and Elsa L. Gunter

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

Abstract

LLVM [Lattner and Adve, 2004] is designed for the compile-time, link-time and run-time optimization of programs written in various programming languages. The language supported by LLVM targeted by modern compilers is LLVM IR [llvm.org, 2018]. In this paper we define K-LLVM, a reference semantics for LLVM IR. To the best of our knowledge, K-LLVM is the most complete formal LLVM IR semantics to date, including all LLVM IR instructions, intrinsic functions in the LLVM documentation and Standard-C library functions that are necessary to execute many LLVM IR programs. Additionally, K-LLVM formulates an abstract machine that executes all LLVM IR instructions. The machine allows to describe our formal semantics in terms of simulating a conceptual virtual machine that runs LLVM IR programs, including non-deterministic programs. Even though the K-LLVM memory model in this paper is assumed to be a sequentially consistent memory model and does not include all LLVM concurrency memory behaviors, the design of K-LLVM’s data layout allows the K-LLVM abstract machine to execute some LLVM IR programs that previous semantics did not cover, such as the full range of LLVM IR behaviors for the interaction among LLVM IR casting, pointer arithmetic, memory operations and some memory flags (e.g. readonly) of function headers. Additionally, the memory model is modularized in a manner that supports investigating other memory models. To validate K-LLVM, we have implemented it in 𝕂 [Roşu, 2016], which generated an interpreter for LLVM IR. Using this, we ran tests including 1,385 unit test programs and around 3,000 concrete LLVM IR programs, and K-LLVM passed all of them.

Cite as

Liyi Li and Elsa L. Gunter. K-LLVM: A Relatively Complete Semantics of LLVM IR. In 34th European Conference on Object-Oriented Programming (ECOOP 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 166, pp. 7:1-7:29, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

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@InProceedings{li_et_al:LIPIcs.ECOOP.2020.7,
  author =	{Li, Liyi and Gunter, Elsa L.},
  title =	{{K-LLVM: A Relatively Complete Semantics of LLVM IR}},
  booktitle =	{34th European Conference on Object-Oriented Programming (ECOOP 2020)},
  pages =	{7:1--7:29},
  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-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.ECOOP.2020.7},
  URN =		{urn:nbn:de:0030-drops-131649},
  doi =		{10.4230/LIPIcs.ECOOP.2020.7},
  annote =	{Keywords: LLVM, formal semantics, K framework, memory model, abstract machine}
}

Document

DOI: 10.4230/LIPIcs.ECOOP.2020.8

Space-Efficient Gradual Typing in Coercion-Passing Style

Authors: Yuya Tsuda, Atsushi Igarashi, and Tomoya Tabuchi

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

Abstract

Herman et al. pointed out that the insertion of run-time checks into a gradually typed program could hamper tail-call optimization and, as a result, worsen the space complexity of the program. To address the problem, they proposed a space-efficient coercion calculus, which was subsequently improved by Siek et al. The semantics of these calculi involves eager composition of run-time checks expressed by coercions to prevent the size of a term from growing. However, it relies also on a nonstandard reduction rule, which does not seem easy to implement. In fact, no compiler implementation of gradually typed languages fully supports the space-efficient semantics faithfully. In this paper, we study coercion-passing style, which Herman et al. have already mentioned, as a technique for straightforward space-efficient implementation of gradually typed languages. A program in coercion-passing style passes "the rest of the run-time checks" around - just like continuation-passing style (CPS), in which "the rest of the computation" is passed around - and (unlike CPS) composes coercions eagerly. We give a formal coercion-passing translation from λS by Siek et al. to λS₁, which is a new calculus of first-class coercions tailored for coercion-passing style, and prove correctness of the translation. We also implement our coercion-passing style transformation for the Grift compiler developed by Kuhlenschmidt et al. An experimental result shows stack overflow can be prevented properly at the cost of up to 3 times slower execution for most partially typed practical programs.

Cite as

Yuya Tsuda, Atsushi Igarashi, and Tomoya Tabuchi. Space-Efficient Gradual Typing in Coercion-Passing Style. In 34th European Conference on Object-Oriented Programming (ECOOP 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 166, pp. 8:1-8:29, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

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@InProceedings{tsuda_et_al:LIPIcs.ECOOP.2020.8,
  author =	{Tsuda, Yuya and Igarashi, Atsushi and Tabuchi, Tomoya},
  title =	{{Space-Efficient Gradual Typing in Coercion-Passing Style}},
  booktitle =	{34th European Conference on Object-Oriented Programming (ECOOP 2020)},
  pages =	{8:1--8:29},
  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-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.ECOOP.2020.8},
  URN =		{urn:nbn:de:0030-drops-131658},
  doi =		{10.4230/LIPIcs.ECOOP.2020.8},
  annote =	{Keywords: Gradual typing, coercion calculus, coercion-passing style, dynamic type checking, tail-call optimization}
}

Document

DOI: 10.4230/LIPIcs.ECOOP.2020.9

Multiparty Session Programming With Global Protocol Combinators

Authors: Keigo Imai, Rumyana Neykova, Nobuko Yoshida, and Shoji Yuen

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

Abstract

Multiparty Session Types (MPST) is a typing discipline for communication protocols. It ensures the absence of communication errors and deadlocks for well-typed communicating processes. The state-of-the-art implementations of the MPST theory rely on (1) runtime linearity checks to ensure correct usage of communication channels and (2) external domain-specific languages for specifying and verifying multiparty protocols. To overcome these limitations, we propose a library for programming with global combinators - a set of functions for writing and verifying multiparty protocols in OCaml. Local behaviours for all processes in a protocol are inferred at once from a global combinator. We formalise global combinators and prove a sound realisability of global combinators - a well-typed global combinator derives a set of local types, by which typed endpoint programs can ensure type and communication safety. Our approach enables fully-static verification and implementation of the whole protocol, from the protocol specification to the process implementations, to happen in the same language. We compare our implementation to untyped and continuation-passing style implementations, and demonstrate its expressiveness by implementing a plethora of protocols. We show our library can interoperate with existing libraries and services, implementing DNS (Domain Name Service) protocol and the OAuth (Open Authentication) protocol.

Cite as

Keigo Imai, Rumyana Neykova, Nobuko Yoshida, and Shoji Yuen. Multiparty Session Programming With Global Protocol Combinators. In 34th European Conference on Object-Oriented Programming (ECOOP 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 166, pp. 9:1-9:30, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

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@InProceedings{imai_et_al:LIPIcs.ECOOP.2020.9,
  author =	{Imai, Keigo and Neykova, Rumyana and Yoshida, Nobuko and Yuen, Shoji},
  title =	{{Multiparty Session Programming With Global Protocol Combinators}},
  booktitle =	{34th European Conference on Object-Oriented Programming (ECOOP 2020)},
  pages =	{9:1--9:30},
  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-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.ECOOP.2020.9},
  URN =		{urn:nbn:de:0030-drops-131662},
  doi =		{10.4230/LIPIcs.ECOOP.2020.9},
  annote =	{Keywords: Multiparty Session Types, Communication Protocol, Concurrent and Distributed Programming, OCaml}
}

Document

Pearl

DOI: 10.4230/LIPIcs.ECOOP.2020.10

Designing with Static Capabilities and Effects: Use, Mention, and Invariants (Pearl)

Authors: Colin S. Gordon

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

Abstract

Capabilities (whether object or reference capabilities) are fundamentally tools to restrict effects. Thus static capabilities (object or reference) and effect systems take different technical machinery to the same core problem of statically restricting or reasoning about effects in programs. Any time two approaches can in principle address the same sets of problems, it becomes important to understand the trade-offs between the approaches, how these trade-offs might interact with the problem at hand. Experts who have worked in these areas tend to find the trade-offs somewhat obvious, having considered them in context before. However, this kind of design discussion is often written down only implicitly as comparison between two approaches for a specific program reasoning problem, rather than as a discussion of general trade-offs between general classes of techniques. As a result, it is not uncommon to set out to solve a problem with one technique, only to find the other better-suited. We discuss the trade-offs between static capabilities (specifically reference capabilities) and effect systems, articulating the challenges each approach tends to have in isolation, and how these are sometimes mitigated. We also put our discussion in context, by appealing to examples of how these trade-offs were considered in the course of developing prior systems in the area. Along the way, we highlight how seemingly-minor aspects of type systems - weakening/framing and the mere existence of type contexts - play a subtle role in the efficacy of these systems.

Cite as

Colin S. Gordon. Designing with Static Capabilities and Effects: Use, Mention, and Invariants (Pearl). In 34th European Conference on Object-Oriented Programming (ECOOP 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 166, pp. 10:1-10:25, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

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@InProceedings{gordon:LIPIcs.ECOOP.2020.10,
  author =	{Gordon, Colin S.},
  title =	{{Designing with Static Capabilities and Effects: Use, Mention, and Invariants}},
  booktitle =	{34th European Conference on Object-Oriented Programming (ECOOP 2020)},
  pages =	{10:1--10:25},
  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.2020.10},
  URN =		{urn:nbn:de:0030-drops-131677},
  doi =		{10.4230/LIPIcs.ECOOP.2020.10},
  annote =	{Keywords: Effect systems, reference capabilities, object capabilities}
}

Document

DOI: 10.4230/LIPIcs.ECOOP.2020.11

Owicki-Gries Reasoning for C11 RAR

Authors: Sadegh Dalvandi, Simon Doherty, Brijesh Dongol, and Heike Wehrheim

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

Abstract

Owicki-Gries reasoning for concurrent programs uses Hoare logic together with an interference freedom rule for concurrency. In this paper, we develop a new proof calculus for the C11 RAR memory model (a fragment of C11 with both relaxed and release-acquire accesses) that allows all Owicki-Gries proof rules for compound statements, including non-interference, to remain unchanged. Our proof method features novel assertions specifying thread-specific views on the state of programs. This is combined with a set of Hoare logic rules that describe how these assertions are affected by atomic program steps. We demonstrate the utility of our proof calculus by verifying a number of standard C11 litmus tests and Peterson’s algorithm adapted for C11. Our proof calculus and its application to program verification have been fully mechanised in the theorem prover Isabelle.

Cite as

Sadegh Dalvandi, Simon Doherty, Brijesh Dongol, and Heike Wehrheim. Owicki-Gries Reasoning for C11 RAR. In 34th European Conference on Object-Oriented Programming (ECOOP 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 166, pp. 11:1-11:26, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

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@InProceedings{dalvandi_et_al:LIPIcs.ECOOP.2020.11,
  author =	{Dalvandi, Sadegh and Doherty, Simon and Dongol, Brijesh and Wehrheim, Heike},
  title =	{{Owicki-Gries Reasoning for C11 RAR}},
  booktitle =	{34th European Conference on Object-Oriented Programming (ECOOP 2020)},
  pages =	{11:1--11:26},
  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.2020.11},
  URN =		{urn:nbn:de:0030-drops-131687},
  doi =		{10.4230/LIPIcs.ECOOP.2020.11},
  annote =	{Keywords: C11, Verification, Hoare logic, Owicki-Gries, Isabelle}
}

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}
}

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