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Documents authored by Gordon, Colin S.

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.
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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.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.2020.23
Lifting Sequential Effects to Control Operators

Authors: Colin S. Gordon

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

Abstract
Sequential effect systems are a class of effect system that exploits information about program order, rather than discarding it as traditional commutative effect systems do. This extra expressive power allows effect systems to reason about behavior over time, capturing properties such as atomicity, unstructured lock ownership, or even general safety properties. While we now understand the essential denotational (categorical) models fairly well, application of these ideas to real software is hampered by the variety of source level control flow constructs and control operators in real languages. We address this new problem by appeal to a classic idea: macro-expression of commonly-used programming constructs in terms of control operators. We give an effect system for a subset of Racket’s tagged delimited control operators, as a lifting of an effect system for a language without direct control operators. This gives the first account of sequential effects in the presence of general control operators. Using this system, we also re-derive the sequential effect system rules for control flow constructs previously shown sound directly, and derive sequential effect rules for new constructs not previously studied in the context of source-level sequential effect systems. This offers a way to directly extend source-level support for sequential effect systems to real programming languages.
Cite as

Colin S. Gordon. Lifting Sequential Effects to Control Operators. In 34th European Conference on Object-Oriented Programming (ECOOP 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 166, pp. 23:1-23:30, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

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@InProceedings{gordon:LIPIcs.ECOOP.2020.23,
  author =	{Gordon, Colin S.},
  title =	{{Lifting Sequential Effects to Control Operators}},
  booktitle =	{34th European Conference on Object-Oriented Programming (ECOOP 2020)},
  pages =	{23:1--23:30},
  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.2020.23},
  URN =		{urn:nbn:de:0030-drops-131804},
  doi =		{10.4230/LIPIcs.ECOOP.2020.23},
  annote =	{Keywords: Type systems, effect systems, quantales, control operators, delimited continuations}
}
Document
DOI: 10.4230/LIPIcs.ECOOP.2017.13
A Generic Approach to Flow-Sensitive Polymorphic Effects

Authors: Colin S. Gordon

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

Abstract
Effect systems are lightweight extensions to type systems that can verify a wide range of important properties with modest developer burden. But our general understanding of effect systems is limited primarily to systems where the order of effects is irrelevant. Understanding such systems in terms of a lattice of effects grounds understanding of the essential issues, and provides guidance when designing new effect systems. By contrast, sequential effect systems --- where the order of effects is important --- lack a clear algebraic characterization. We derive an algebraic characterization from the shape of prior concrete sequential effect systems. We present an abstract polymorphic effect system with singleton effects parameterized by an effect quantale --- an algebraic structure with well-defined properties that can model a range of existing order-sensitive effect systems. We define effect quantales, derive useful properties, and show how they cleanly model a variety of known sequential effect systems. We show that effect quantales provide a free, general notion of iterating a sequential effect, and that for systems we consider the derived iteration agrees with the manually designed iteration operators in prior work. Identifying and applying the right algebraic structure led us to subtle insights into the design of order-sensitive effect systems, which provides guidance on non-obvious points of designing order-sensitive effect systems. Effect quantales have clear relationships to the recent category theoretic work on order-sensitive effect systems, but are explained without recourse to category theory. In addition, our derived iteration construct should generalize to these semantic structures, addressing limitations of that work.
Cite as

Colin S. Gordon. A Generic Approach to Flow-Sensitive Polymorphic Effects. In 31st European Conference on Object-Oriented Programming (ECOOP 2017). Leibniz International Proceedings in Informatics (LIPIcs), Volume 74, pp. 13:1-13:31, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2017)

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@InProceedings{gordon:LIPIcs.ECOOP.2017.13,
  author =	{Gordon, Colin S.},
  title =	{{A Generic Approach to Flow-Sensitive Polymorphic Effects}},
  booktitle =	{31st European Conference on Object-Oriented Programming (ECOOP 2017)},
  pages =	{13:1--13:31},
  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.2017.13},
  URN =		{urn:nbn:de:0030-drops-72561},
  doi =		{10.4230/LIPIcs.ECOOP.2017.13},
  annote =	{Keywords: Type systems, effect systems, quantales, polymorphism}
}
Document
DOI: 10.4230/LIPIcs.ECOOP.2016.1
Trace Typing: An Approach for Evaluating Retrofitted Type Systems

Authors: Esben Andreasen, Colin S. Gordon, Satish Chandra, Manu Sridharan, Frank Tip, and Koushik Sen

Published in: LIPIcs, Volume 56, 30th European Conference on Object-Oriented Programming (ECOOP 2016)

Abstract
Recent years have seen growing interest in the retrofitting of type systems onto dynamically-typed programming languages, in order to improve type safety, programmer productivity, or performance. In such cases, type system developers must strike a delicate balance between disallowing certain coding patterns to keep the type system simple, or including them at the expense of additional complexity and effort. Thus far, the process for designing retrofitted type systems has been largely ad hoc, because evaluating multiple variations of a type system on large bodies of existing code is a significant undertaking. We present trace typing: a framework for automatically and quantitatively evaluating variations of a retrofitted type system on large code bases. The trace typing approach involves gathering traces of program executions, inferring types for instances of variables and expressions occurring in a trace, and merging types according to merge strategies that reflect specific (combinations of) choices in the source-level type system design space. We evaluated trace typing through several experiments. We compared several variations of type systems retrofitted onto JavaScript, measuring the number of program locations with type errors in each case on a suite of over fifty thousand lines of JavaScript code. We also used trace typing to validate and guide the design of a new retrofitted type system that enforces fixed object layout for JavaScript objects. Finally, we leveraged the types computed by trace typing to automatically identify tag tests --- dynamic checks that refine a type --- and examined the variety of tests identified.
Cite as

Esben Andreasen, Colin S. Gordon, Satish Chandra, Manu Sridharan, Frank Tip, and Koushik Sen. Trace Typing: An Approach for Evaluating Retrofitted Type Systems. In 30th European Conference on Object-Oriented Programming (ECOOP 2016). Leibniz International Proceedings in Informatics (LIPIcs), Volume 56, pp. 1:1-1:26, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2016)

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@InProceedings{andreasen_et_al:LIPIcs.ECOOP.2016.1,
  author =	{Andreasen, Esben and Gordon, Colin S. and Chandra, Satish and Sridharan, Manu and Tip, Frank and Sen, Koushik},
  title =	{{Trace Typing: An Approach for Evaluating Retrofitted Type Systems}},
  booktitle =	{30th European Conference on Object-Oriented Programming (ECOOP 2016)},
  pages =	{1:1--1:26},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-014-9},
  ISSN =	{1868-8969},
  year =	{2016},
  volume =	{56},
  editor =	{Krishnamurthi, Shriram and Lerner, Benjamin S.},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ECOOP.2016.1},
  URN =		{urn:nbn:de:0030-drops-60952},
  doi =		{10.4230/LIPIcs.ECOOP.2016.1},
  annote =	{Keywords: Retrofitted type systems, Type system design, trace typing}
}
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