23 Search Results for "Ahmed, Amal"

Document
DOI: 10.4230/DagRep.15.6.51
Utilising and Scaling the WebAssembly Semantics (Dagstuhl Seminar 25241)

Authors: Amal Ahmed, Andreas Rossberg, Deian Stefan, Conrad Watt, and Michelle Thalakottur

Published in: Dagstuhl Reports, Volume 15, Issue 6 (2026)

Abstract
WebAssembly (Wasm) is a safe and portable, low level bytecode format used in browsers, IoT applications, cloud, edge, embedded systems and blockchains. Its popularity as a technology for both practically building and theoretically investigating verified and secure systems has been growing rapidly. This Dagstuhl Seminar brought together leading academics and industry representatives involved in Wasm, both as designers, implementers or clients of the technology, to exchange ideas around topics such as tools for formal specification, verified compilation, software fault isolation and language interoperability.
Cite as

Amal Ahmed, Andreas Rossberg, Deian Stefan, Conrad Watt, and Michelle Thalakottur. Utilising and Scaling the WebAssembly Semantics (Dagstuhl Seminar 25241). In Dagstuhl Reports, Volume 15, Issue 6, pp. 51-68, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)

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@Article{ahmed_et_al:DagRep.15.6.51,
  author =	{Ahmed, Amal and Rossberg, Andreas and Stefan, Deian and Watt, Conrad and Thalakottur, Michelle},
  title =	{{Utilising and Scaling the WebAssembly Semantics (Dagstuhl Seminar 25241)}},
  pages =	{51--68},
  journal =	{Dagstuhl Reports},
  ISSN =	{2192-5283},
  year =	{2026},
  volume =	{15},
  number =	{6},
  editor =	{Ahmed, Amal and Rossberg, Andreas and Stefan, Deian and Watt, Conrad and Thalakottur, Michelle},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/DagRep.15.6.51},
  URN =		{urn:nbn:de:0030-drops-255770},
  doi =		{10.4230/DagRep.15.6.51},
  annote =	{Keywords: Compilers, Formal Methods, JavaScript, Proof Assistants, Runtimes, Software Verification, Webassembly}
}
Document
DOI: 10.4230/OASIcs.Programming.2025.20
On the Effectiveness of Interpreter-Guided Compiler Testing

Authors: Federico Lochbaum and Guillermo Polito

Published in: OASIcs, Volume 134, Companion Proceedings of the 9th International Conference on the Art, Science, and Engineering of Programming (Programming 2025)

Abstract
Guaranteeing that a compiler behaves correctly is a complex task often approached through test generation and fuzzing. Compiler test generation must not only ensure that a compiler generates code that does not break, but also that it implements the programming language semantics. Recently, interpreter-guided test generation has been proposed to test JIT compilers: Concolic-execution on the interpreter yields test cases for the language semantics which are then validated between differential testing of the interpreter and compiler. In previous work, this solution has been shown to find interpreter/compiler differences. However, little has been said about the effectiveness and the solution limits. In this paper we study the behavior of this technique, to shed light on future improvements and research. We experiment with this technique on the JIT compiler for the Pharo programming language, on two different backends: ARMv7 and x86. We explore how effective the solution is in terms of compiler coverage and its limitations, and we discuss how future research can overcome them. Moreover, we investigate how this technique combined with random constraint mutations increases backend compiler coverage.
Cite as

Federico Lochbaum and Guillermo Polito. On the Effectiveness of Interpreter-Guided Compiler Testing. In Companion Proceedings of the 9th International Conference on the Art, Science, and Engineering of Programming (Programming 2025). Open Access Series in Informatics (OASIcs), Volume 134, pp. 20:1-20:15, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{lochbaum_et_al:OASIcs.Programming.2025.20,
  author =	{Lochbaum, Federico and Polito, Guillermo},
  title =	{{On the Effectiveness of Interpreter-Guided Compiler Testing}},
  booktitle =	{Companion Proceedings of the 9th International Conference on the Art, Science, and Engineering of Programming (Programming 2025)},
  pages =	{20:1--20:15},
  series =	{Open Access Series in Informatics (OASIcs)},
  ISBN =	{978-3-95977-382-9},
  ISSN =	{2190-6807},
  year =	{2025},
  volume =	{134},
  editor =	{Edwards, Jonathan and Perera, Roly and Petricek, Tomas},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/OASIcs.Programming.2025.20},
  URN =		{urn:nbn:de:0030-drops-243040},
  doi =		{10.4230/OASIcs.Programming.2025.20},
  annote =	{Keywords: Virtual Machines, Concolic Testing, JIT compilers, interpreters, Differential Testing, Constraint Mutations, Compiler Coverage}
}
Document
Extended Abstract
DOI: 10.4230/OASIcs.Programming.2025.24
Toward a Typed Intermediate Language for R (Extended Abstract)

Authors: Mickaël Laurent, Jakob Hain, Filip Krikava, Sebastián Krynski, and Jan Vitek

Published in: OASIcs, Volume 134, Companion Proceedings of the 9th International Conference on the Art, Science, and Engineering of Programming (Programming 2025)

Abstract
Compilers for dynamic languages often rely on intermediate representations with explicit type annotations to facilitate writing program transformations. This paper documents the design of a new typed intermediate representation for a just-in-time compiler for the R programming language called FIŘ. Type annotations, in FIŘ, capture properties such as sharing, the potential for effects, and compiler speculations. In this extended abstract, we focus on the sharing properties that may be used to optimize away some copies of values.
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Mickaël Laurent, Jakob Hain, Filip Krikava, Sebastián Krynski, and Jan Vitek. Toward a Typed Intermediate Language for R (Extended Abstract). In Companion Proceedings of the 9th International Conference on the Art, Science, and Engineering of Programming (Programming 2025). Open Access Series in Informatics (OASIcs), Volume 134, pp. 24:1-24:4, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{laurent_et_al:OASIcs.Programming.2025.24,
  author =	{Laurent, Micka\"{e}l and Hain, Jakob and Krikava, Filip and Krynski, Sebasti\'{a}n and Vitek, Jan},
  title =	{{Toward a Typed Intermediate Language for R}},
  booktitle =	{Companion Proceedings of the 9th International Conference on the Art, Science, and Engineering of Programming (Programming 2025)},
  pages =	{24:1--24:4},
  series =	{Open Access Series in Informatics (OASIcs)},
  ISBN =	{978-3-95977-382-9},
  ISSN =	{2190-6807},
  year =	{2025},
  volume =	{134},
  editor =	{Edwards, Jonathan and Perera, Roly and Petricek, Tomas},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/OASIcs.Programming.2025.24},
  URN =		{urn:nbn:de:0030-drops-243086},
  doi =		{10.4230/OASIcs.Programming.2025.24},
  annote =	{Keywords: JIT, compilation, static typing, ownership, copy-on-write, dynamic language}
}
Document
DOI: 10.4230/LIPIcs.FSCD.2025.4
Substructural Parametricity

Authors: C. B. Aberlé, Karl Crary, Chris Martens, and Frank Pfenning

Published in: LIPIcs, Volume 337, 10th International Conference on Formal Structures for Computation and Deduction (FSCD 2025)

Abstract
Ordered, linear, and other substructural type systems allow us to expose deep properties of programs at the syntactic level of types. In this paper, we develop a family of unary logical relations that allow us to prove consequences of parametricity for a range of substructural type systems. A key idea is to parameterize the relation by an algebra, which we exemplify with a monoid and commutative monoid to interpret ordered and linear type systems, respectively. We prove the fundamental theorem of logical relations and apply it to deduce extensional properties of inhabitants of certain types. Examples include demonstrating that the ordered types for list append and reversal are inhabited by exactly one function, as are types of some tree traversals. Similarly, the linear type of the identity function on lists is inhabited only by permutations of the input. Our most advanced example shows that the ordered type of the list fold function is inhabited only by the fold function.
Cite as

C. B. Aberlé, Karl Crary, Chris Martens, and Frank Pfenning. Substructural Parametricity. In 10th International Conference on Formal Structures for Computation and Deduction (FSCD 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 337, pp. 4:1-4:21, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{aberle_et_al:LIPIcs.FSCD.2025.4,
  author =	{Aberl\'{e}, C. B. and Crary, Karl and Martens, Chris and Pfenning, Frank},
  title =	{{Substructural Parametricity}},
  booktitle =	{10th International Conference on Formal Structures for Computation and Deduction (FSCD 2025)},
  pages =	{4:1--4:21},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-374-4},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{337},
  editor =	{Fern\'{a}ndez, Maribel},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.FSCD.2025.4},
  URN =		{urn:nbn:de:0030-drops-236193},
  doi =		{10.4230/LIPIcs.FSCD.2025.4},
  annote =	{Keywords: Substructural type systems, logical relations, ordered logic}
}
Document
DOI: 10.4230/LIPIcs.FSCD.2025.15
On the Metric Nature of (Differential) Logical Relations

Authors: Ugo Dal Lago, Naohiko Hoshino, and Paolo Pistone

Published in: LIPIcs, Volume 337, 10th International Conference on Formal Structures for Computation and Deduction (FSCD 2025)

Abstract
Differential logical relations are a method to measure distances between higher-order programs. They differ from standard methods based on program metrics in that differences between functional programs are themselves functions, relating errors in input with errors in output, this way providing a more fine grained, contextual, information. The aim of this paper is to clarify the metric nature of differential logical relations. While previous work has shown that these do not give rise, in general, to (quasi-)metric spaces nor to partial metric spaces, we show that the distance functions arising from such relations, that we call quasi-quasi-metrics, can be related to both quasi-metrics and partial metrics, the latter being also captured by suitable relational definitions. Moreover, we exploit such connections to deduce some new compositional reasoning principles for program differences.
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Ugo Dal Lago, Naohiko Hoshino, and Paolo Pistone. On the Metric Nature of (Differential) Logical Relations. In 10th International Conference on Formal Structures for Computation and Deduction (FSCD 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 337, pp. 15:1-15:22, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{dallago_et_al:LIPIcs.FSCD.2025.15,
  author =	{Dal Lago, Ugo and Hoshino, Naohiko and Pistone, Paolo},
  title =	{{On the Metric Nature of (Differential) Logical Relations}},
  booktitle =	{10th International Conference on Formal Structures for Computation and Deduction (FSCD 2025)},
  pages =	{15:1--15:22},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-374-4},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{337},
  editor =	{Fern\'{a}ndez, Maribel},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.FSCD.2025.15},
  URN =		{urn:nbn:de:0030-drops-236300},
  doi =		{10.4230/LIPIcs.FSCD.2025.15},
  annote =	{Keywords: Differential Logical Relations, Quantales, Quasi-Metrics, Partial Metrics}
}
Document
DOI: 10.4230/LIPIcs.FSCD.2025.33
Solving Guarded Domain Equations in Presheaves over Ordinals and Mechanizing It

Authors: Sergei Stepanenko and Amin Timany

Published in: LIPIcs, Volume 337, 10th International Conference on Formal Structures for Computation and Deduction (FSCD 2025)

Abstract
Constructing solutions to recursive domain equations is a well-known, important problem in the study of programs and programming languages. Mathematically speaking, the problem is finding a fixed point (up to isomorphism) of a suitable functor over a suitable category. A particularly useful instance, inspired by the step-indexing technique, is where the functor is over (a subcategory of) the category of presheaves over the ordinal ω and the functors are locally-contractive, also known as guarded functors. This corresponds to step-indexing over natural numbers. However, for certain problems, e.g., when dealing with infinite non-determinism, one needs to employ trans-finite step-indexing, i.e., consider presheaf categories over higher ordinals. Prior work on trans-finite step-indexing either only considers a very narrow class of functors over a particularly restricted subcategory of presheaves over higher ordinals, or treats the problem very generally working with sheaves over an arbitrary complete Heyting algebra with a well-founded basis. In this paper we present a solution to the guarded domain equations problem over all guarded functors over the category of presheaves over ordinal numbers, as well as its mechanization in the Rocq Prover. As the categories of sheaves and presheaves over ordinals are equivalent, our main contribution is simplifying prior work from the setting of the category of sheaves to the setting of the category of presheaves and mechanizing it - presheaves are more amenable to mechanization in a proof assistant.
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Sergei Stepanenko and Amin Timany. Solving Guarded Domain Equations in Presheaves over Ordinals and Mechanizing It. In 10th International Conference on Formal Structures for Computation and Deduction (FSCD 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 337, pp. 33:1-33:24, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{stepanenko_et_al:LIPIcs.FSCD.2025.33,
  author =	{Stepanenko, Sergei and Timany, Amin},
  title =	{{Solving Guarded Domain Equations in Presheaves over Ordinals and Mechanizing It}},
  booktitle =	{10th International Conference on Formal Structures for Computation and Deduction (FSCD 2025)},
  pages =	{33:1--33:24},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-374-4},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{337},
  editor =	{Fern\'{a}ndez, Maribel},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.FSCD.2025.33},
  URN =		{urn:nbn:de:0030-drops-236486},
  doi =		{10.4230/LIPIcs.FSCD.2025.33},
  annote =	{Keywords: Domain Equations, Guarded Fixed Points, Fixed Points, Category Theory, Rocq, Presheaves, Ordinals}
}
Document
Survey
DOI: 10.4230/TGDK.3.1.3
Uncertainty Management in the Construction of Knowledge Graphs: A Survey

Authors: Lucas Jarnac, Yoan Chabot, and Miguel Couceiro

Published in: TGDK, Volume 3, Issue 1 (2025). Transactions on Graph Data and Knowledge, Volume 3, Issue 1

Abstract
Knowledge Graphs (KGs) are a major asset for companies thanks to their great flexibility in data representation and their numerous applications, e.g., vocabulary sharing, Q&A or recommendation systems. To build a KG, it is a common practice to rely on automatic methods for extracting knowledge from various heterogeneous sources. However, in a noisy and uncertain world, knowledge may not be reliable and conflicts between data sources may occur. Integrating unreliable data would directly impact the use of the KG, therefore such conflicts must be resolved. This could be done manually by selecting the best data to integrate. This first approach is highly accurate, but costly and time-consuming. That is why recent efforts focus on automatic approaches, which represent a challenging task since it requires handling the uncertainty of extracted knowledge throughout its integration into the KG. We survey state-of-the-art approaches in this direction and present constructions of both open and enterprise KGs. We then describe different knowledge extraction methods and discuss downstream tasks after knowledge acquisition, including KG completion using embedding models, knowledge alignment, and knowledge fusion in order to address the problem of knowledge uncertainty in KG construction. We conclude with a discussion on the remaining challenges and perspectives when constructing a KG taking into account uncertainty.
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Lucas Jarnac, Yoan Chabot, and Miguel Couceiro. Uncertainty Management in the Construction of Knowledge Graphs: A Survey. In Transactions on Graph Data and Knowledge (TGDK), Volume 3, Issue 1, pp. 3:1-3:48, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@Article{jarnac_et_al:TGDK.3.1.3,
  author =	{Jarnac, Lucas and Chabot, Yoan and Couceiro, Miguel},
  title =	{{Uncertainty Management in the Construction of Knowledge Graphs: A Survey}},
  journal =	{Transactions on Graph Data and Knowledge},
  pages =	{3:1--3:48},
  ISSN =	{2942-7517},
  year =	{2025},
  volume =	{3},
  number =	{1},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/TGDK.3.1.3},
  URN =		{urn:nbn:de:0030-drops-233733},
  doi =		{10.4230/TGDK.3.1.3},
  annote =	{Keywords: Knowledge reconciliation, Uncertainty, Heterogeneous sources, Knowledge graph construction}
}
Document
DOI: 10.4230/DagRep.11.6.54
Scalable Handling of Effects (Dagstuhl Seminar 21292)

Authors: Danel Ahman, Amal Ahmed, Sam Lindley, and Andreas Rossberg

Published in: Dagstuhl Reports, Volume 11, Issue 6 (2021)

Abstract
Built on solid mathematical foundations, effect handlers offer a uniform and elegant approach to programming with user-defined computational effects. They subsume many widely used programming concepts and abstractions, such as actors, async/await, backtracking, coroutines, generators/iterators, and probabilistic programming. As such, they allow language implementers to target a single implementation of effect handlers, freeing language implementers from having to maintain separate ad hoc implementations of each of the features listed above. Due to their wide applicability, effect handlers are enjoying growing interest in academia and industry. For instance, several effect handler oriented research languages are under active development (such as Eff, Frank, and Koka), as are effect handler libraries for mainstream languages (such as C and Java), effect handlers are seeing increasing use in probabilistic programming tools (such as Uber’s Pyro), and proposals are in the pipeline to include them natively in low-level languages (such as WebAssembly). Effect handlers are also a key part of Multicore OCaml, which incorporates an efficient implementation of them for uniformly expressing user-definable concurrency models in the language. However, enabling effect handlers to scale requires tackling some hard problems, both in theory and in practice. Inspired by experience of developing, programming with, and reasoning about effect handlers in practice, we identify five key problem areas to be addressed at this Dagstuhl Seminar in order to enable effect handlers to scale: Safety, Modularity, Interoperability, Legibility, and Efficiency. In particular, we seek answers to the following questions: - How can we enforce safe interaction between effect handler programs and external resources? - How can we enable modular use of effect handlers for programming in the large? - How can we support interoperable effect handler programs written in different languages? - How can we write legible effect handler programs in a style accessible to mainstream programmers? - How can we generate efficient code from effect handler programs?
Cite as

Danel Ahman, Amal Ahmed, Sam Lindley, and Andreas Rossberg. Scalable Handling of Effects (Dagstuhl Seminar 21292). In Dagstuhl Reports, Volume 11, Issue 6, pp. 54-81, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)

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@Article{ahman_et_al:DagRep.11.6.54,
  author =	{Ahman, Danel and Ahmed, Amal and Lindley, Sam and Rossberg, Andreas},
  title =	{{Scalable Handling of Effects (Dagstuhl Seminar 21292)}},
  pages =	{54--81},
  journal =	{Dagstuhl Reports},
  ISSN =	{2192-5283},
  year =	{2021},
  volume =	{11},
  number =	{6},
  editor =	{Ahman, Danel and Ahmed, Amal and Lindley, Sam and Rossberg, Andreas},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/DagRep.11.6.54},
  URN =		{urn:nbn:de:0030-drops-155800},
  doi =		{10.4230/DagRep.11.6.54},
  annote =	{Keywords: continuations, Effect handlers, Wasm}
}
Document
SCICO Journal-first
DOI: 10.4230/LIPIcs.ECOOP.2020.33
Abstracting Gradual References (SCICO Journal-first)

Authors: Matías Toro and Éric Tanter

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

Abstract
Gradual typing is an effective approach to integrate static and dynamic typing, which supports the smooth transition between both extremes via the (programmer-controlled) precision of type annotations [Jeremy Siek and Walid Taha, 2006; Siek et al., 2015]. Imprecision is normally introduced via the unknown type ?, e.g. function type Int → Bool is more precise than ? → ?, and both more precise than ?. Gradual typing relates types of different precision using consistent type relations, such as type consistency (resp. consistent subtyping), the gradual counterpart of type equality (resp. subtyping). For instance, ? → Int is consistent with Bool → ?. This approach has been applied in a number of settings, such as objects [Jeremy Siek and Walid Taha, 2007], subtyping [Jeremy Siek and Walid Taha, 2007; Ronald Garcia et al., 2016], effects [Bañados Schwerter et al., 2014; Bañados Schwerter et al., 2016], ownership [Ilya Sergey and Dave Clarke, 2012], typestates [Roger Wolff et al., 2011; Ronald Garcia et al., 2014], information-flow typing [Tim Disney and Cormac Flanagan, 2011; Luminous Fennell and Peter Thiemann, 2013; Matías Toro et al., 2018], session types [Igarashi et al., 2017], refinements [Nico Lehmann and {É}ric Tanter, 2017], set-theoretic types [Castagna and Lanvin, 2017], Hoare logic [Johannes Bader et al., 2018], parametric polymorphism [Amal Ahmed et al., 2011; Ahmed et al., 2017; Ina and Igarashi, 2011; Igarashi et al., 2017; Ningning Xie et al., 2018; Matías Toro et al., 2019], and references [Jeremy Siek and Walid Taha, 2006; Herman et al., 2010; Siek et al., 2015]. In particular, gradual typing for mutable references has seen the elaboration of various possible semantics: invariant references [Jeremy Siek and Walid Taha, 2006], guarded references [Herman et al., 2010], monotonic references [Siek et al., 2015], and permissive references [Siek et al., 2015]. Invariant references are a form of references where reference types are invariant with respect to type consistency. Guarded references admit variance thanks to systematic runtime checks on reference reads and writes; the runtime type of an allocated cell never changes during execution. Guarded references have been formulated in a space-efficient coercion calculus, which ensures that gradual programs do not accumulate unbounded pending checks during execution. Hereafter, we refer to this language as HCC. Monotonic references favor efficiency over flexibility by only allowing reference cells to vary towards more precise types. This allows reference operations in statically-typed regions to safely proceed without any runtime checks. Permissive references are the most flexible approach, in which reference cells can be initialized and updated to any value of any type at any time. These four developments reflect different design decisions with respect to gradual references: is the reference type constructor variant under consistency? Can the programmer specify a precise bound on the static type of a reference, and hence on the corresponding heap cell type? Can the heap cell type evolve its precision at runtime, and if yes, how? There is obviously no absolute answer to these questions, as they reflect different tradeoffs such as in efficiency and precision. This work explores the semantics that results from the application of a systematic methodology to gradualize static type systems. Currently we can find in the literature two methodologies to gradualize statically-typed languages: Abstracting Gradual Typing (AGT) [Ronald Garcia et al., 2016], and the Gradualizer [Matteo Cimini and Jeremy Siek, 2016]. In this work, we consider the AGT methodology as it naturally scales to auxiliary structures such as a mutable heap. The AGT methodology helps to systematically construct gradually-typed languages by using abstract interpretation [Cousot and Cousot, 1977] at the type level. In brief, AGT interprets gradual types as an abstraction of sets of possible static types, formally captured through a Galois connection. The static semantics of a gradual language are then derived by lifting the semantics of a statically-typed language through this connection, and the dynamic semantics follow by Curry-Howard from proof normalization of the type safety argument. The AGT methodology has been shown to be effective in many contexts: records and subtyping [Ronald Garcia et al., 2016], type-and-effects [Bañados Schwerter et al., 2014; Bañados Schwerter et al., 2016], refinement types [Nico Lehmann and Éric Tanter, 2017; Niki Vazou et al., 2018], set-theoretic and union types [Castagna and Lanvin, 2017; Matías Toro and Éric Tanter, 2017], information-flow typing [Matías Toro et al., 2018], and parametric polymorphism [Matías Toro et al., 2019]. However, this methodology has never been applied to mutable references in isolation. Although Toro et al. [Matías Toro et al., 2018] apply AGT to a language with references, they only gradualize security levels of types (e.g. Ref Int_?), not whole types (e.g. Ref ? is not supported). In this article we answer the following open questions: Which semantics for gradually-type references follows by systematically applying AGT? Does AGT justify one of the existing approaches, or does it suggest yet another design? Can we recover other semantics for gradual references, if yes, how? This article first reviews the different existing gradual approaches to mutable references through examples. It then presents the semantics for gradual references that is obtained by applying AGT, and how to accommodate the other semantics. More specifically, this work makes the following contributions: - We present λ_REF~, a gradual language with support for mutable references. We derive λ_REF~ by applying the AGT methodology to a fully-static simple language with mutable references called λ_REF. This is the first application of AGT that focuses on gradually-typed mutable references. - We prove that λ_REF~ satisfies the gradual guarantee of Siek et al. [Siek et al., 2015]. We also present the first formal statement and proof of the conservative extension of the dynamic semantics of the static language [Siek et al., 2015], for a gradual language derived using AGT. - We prove that the derived language, λ_REF~, corresponds to the semantics of guarded references from HCC. Formally, given a λ_REF~ term and its compilation to HCC^+ (an adapted version of HCC extended with conditionals and binary operations) we prove that both terms are bisimilar, and that consequently they either both terminate, both fail, or both diverge. - We observe that λ_REF~ and HCC^+ differ in the order of combination of runtime checks. As a result, HCC is space efficient whereas λ_REF~ is not: we can write programs in λ_REF~ that may accumulate an unbounded number of checks. We formalize the changes needed in the dynamic semantics of λ_REF~ to achieve space efficiency. This technique to recover space efficiency is in fact independent from mutable references, and is therefore applicable to other gradual languages derived with AGT. - We formally describe how to support other gradual reference semantics in λ_REF~ by presenting λ_REF~^𝗉𝗆, an extension that additionally supports both permissive and monotonic references. Finally, we prove for the first time that monotonic references satisfy the dynamic gradual guarantee, a non-trivial result that requires careful consideration of updates to the store. Additionally, we implemented λ_REF~ as an interactive prototype that displays both typing derivations and reduction traces. All the examples mentioned in this paper are readily available in the online prototype available at https://pleiad.cl/grefs. As a result, this paper sheds further light on the design space of gradual languages with mutable references and contributes to deepening the understanding of the AGT methodology.
Cite as

Matías Toro and Éric Tanter. Abstracting Gradual References (SCICO Journal-first). In 34th European Conference on Object-Oriented Programming (ECOOP 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 166, pp. 33:1-33:4, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

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@InProceedings{toro_et_al:LIPIcs.ECOOP.2020.33,
  author =	{Toro, Mat{\'\i}as and Tanter, \'{E}ric},
  title =	{{Abstracting Gradual References}},
  booktitle =	{34th European Conference on Object-Oriented Programming (ECOOP 2020)},
  pages =	{33:1--33:4},
  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.2020.33},
  URN =		{urn:nbn:de:0030-drops-131900},
  doi =		{10.4230/LIPIcs.ECOOP.2020.33},
  annote =	{Keywords: Gradual Typing, Mutable References, Abstract interpretation}
}
Document
DOI: 10.4230/DagRep.8.5.1
Secure Compilation (Dagstuhl Seminar 18201)

Authors: Amal Ahmed, Deepak Garg, Catalin Hritcu, and Frank Piessens

Published in: Dagstuhl Reports, Volume 8, Issue 5 (2019)

Abstract
Secure compilation is an emerging field that puts together advances in security, programming languages, verification, systems, and hardware architectures in order to devise secure compilation chains that eliminate many of today's vulnerabilities. Secure compilation aims to protect a source language's abstractions in compiled code, even against low-level attacks. For a concrete example, all modern languages provide a notion of structured control flow and an invoked procedure is expected to return to the right place. However, today's compilation chains (compilers, linkers, loaders, runtime systems, hardware) cannot efficiently enforce this abstraction: linked low-level code can call and return to arbitrary instructions or smash the stack, blatantly violating the high-level abstraction. The emerging secure compilation community aims to address such problems by devising formal security criteria, efficient enforcement mechanisms, and effective proof techniques. This seminar strived to take a broad and inclusive view of secure compilation and to provide a forum for discussion on the topic. The goal was to identify interesting research directions and open challenges by bringing together people working on building secure compilation chains, on developing proof techniques and verification tools, and on designing security mechanisms.
Cite as

Amal Ahmed, Deepak Garg, Catalin Hritcu, and Frank Piessens. Secure Compilation (Dagstuhl Seminar 18201). In Dagstuhl Reports, Volume 8, Issue 5, pp. 1-30, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)

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@Article{ahmed_et_al:DagRep.8.5.1,
  author =	{Ahmed, Amal and Garg, Deepak and Hritcu, Catalin and Piessens, Frank},
  title =	{{Secure Compilation (Dagstuhl Seminar 18201)}},
  pages =	{1--30},
  journal =	{Dagstuhl Reports},
  ISSN =	{2192-5283},
  year =	{2018},
  volume =	{8},
  number =	{5},
  editor =	{Ahmed, Amal and Garg, Deepak and Hritcu, Catalin and Piessens, Frank},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/DagRep.8.5.1},
  URN =		{urn:nbn:de:0030-drops-98911},
  doi =		{10.4230/DagRep.8.5.1},
  annote =	{Keywords: secure compilation, low-level attacks, source-level reasoning, attacker models, full abstraction, hyperproperties, enforcement mechanisms, compartmentalization, security architectures, side-channels}
}
Document
DOI: 10.4230/LIPIcs.SNAPL.2017.12
Linking Types for Multi-Language Software: Have Your Cake and Eat It Too

Authors: Daniel Patterson and Amal Ahmed

Published in: LIPIcs, Volume 71, 2nd Summit on Advances in Programming Languages (SNAPL 2017)

Abstract
Large software systems are and should be implemented with many different languages, each suited to the domain of the task at hand. High-level business logic may be written in Java or OCaml, resource-intensive components may be written in C or Rust, and high-assurance components may be written in Coq. In some development shops, domain-specific languages are used in various parts of systems to better separate the logic of particular problems from the plumbing of general-purpose programming. But how are programmers to reason about such multi-language systems? Currently, for a programmer to reason about a single source component within this multi-language system, it is not sufficient for her to consider how her component behaves in source-level contexts. Instead, she is required to understand the target contexts that her component will be run in after compilation - which requires not only understanding aspects of the compiler, but also how target components are linked together. These target contexts may have behavior inexpressible in the source, which can impact the notion of equivalence that justifies behavior-preserving modifications of code, whether programmer refactorings or compiler optimizations. But while programmers should not have to reason about arbitrary target contexts, sometimes multi-language linking is done exactly to gain access to features unavailable in the source. To enable programmers to reason about components that link with behavior inexpressible in their language, we advocate that language designers incorporate specifications for linking into the source language. Such specifications should allow a programmer to reason about inputs from other languages in a way that remains close to the semantics of her language. Linking types are a well-specified minimal extension of a source language that allow programmers to annotate where in their programs they can link with components that are not expressible in their unadulterated source language. This gives them fine-grained control over the contexts that they must reason about and the equivalences that arise.
Cite as

Daniel Patterson and Amal Ahmed. Linking Types for Multi-Language Software: Have Your Cake and Eat It Too. In 2nd Summit on Advances in Programming Languages (SNAPL 2017). Leibniz International Proceedings in Informatics (LIPIcs), Volume 71, pp. 12:1-12:15, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2017)

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@InProceedings{patterson_et_al:LIPIcs.SNAPL.2017.12,
  author =	{Patterson, Daniel and Ahmed, Amal},
  title =	{{Linking Types for Multi-Language Software: Have Your Cake and Eat It Too}},
  booktitle =	{2nd Summit on Advances in Programming Languages (SNAPL 2017)},
  pages =	{12:1--12:15},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-032-3},
  ISSN =	{1868-8969},
  year =	{2017},
  volume =	{71},
  editor =	{Lerner, Benjamin S. and Bod{\'\i}k, Rastislav and Krishnamurthi, Shriram},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.SNAPL.2017.12},
  URN =		{urn:nbn:de:0030-drops-71250},
  doi =		{10.4230/LIPIcs.SNAPL.2017.12},
  annote =	{Keywords: Linking, program reasoning, equivalence, expressive power of languages, fully abstract compilation}
}
Document
DOI: 10.4230/LIPIcs.FSCD.2016.1
Compositional Compiler Verification for a Multi-Language World

Authors: Amal Ahmed

Published in: LIPIcs, Volume 52, 1st International Conference on Formal Structures for Computation and Deduction (FSCD 2016)

Abstract
Verified compilers are typically proved correct under severe restrictions on what the compiler's output may be linked with, from no linking at all to linking only with code compiled from the same source language. Such assumptions contradict the reality of how we use these compilers since most software systems today are comprised of components written in different languages compiled by different compilers to a common target, as well as low-level libraries that may be handwritten in the target language. The key challenge in verifying compilers for today's world of multi-language software is how to formally state a compiler correctness theorem that is compositional along two dimensions. First, the theorem must guarantee correct compilation of components while allowing compiled code to be composed (linked) with target-language components of arbitrary provenance, including those compiled from other languages. Second, the theorem must support verification of multi-pass compilers by composing correctness proofs for individual passes. In this talk, I will describe a methodology for verifying compositional compiler correctness for a higher-order typed language and discuss the challenges that lie ahead. I will argue that compositional compiler correctness is, in essence, a language interoperability problem: for viable solutions in the long term, high-level languages must be equipped with principled foreign-function interfaces that specify safe interoperability between high-level and low-level components, and between more precisely and less precisely typed code.
Cite as

Amal Ahmed. Compositional Compiler Verification for a Multi-Language World. In 1st International Conference on Formal Structures for Computation and Deduction (FSCD 2016). Leibniz International Proceedings in Informatics (LIPIcs), Volume 52, p. 1:1, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2016)

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@InProceedings{ahmed:LIPIcs.FSCD.2016.1,
  author =	{Ahmed, Amal},
  title =	{{Compositional Compiler Verification for a Multi-Language World}},
  booktitle =	{1st International Conference on Formal Structures for Computation and Deduction (FSCD 2016)},
  pages =	{1:1--1:1},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-010-1},
  ISSN =	{1868-8969},
  year =	{2016},
  volume =	{52},
  editor =	{Kesner, Delia and Pientka, Brigitte},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.FSCD.2016.1},
  URN =		{urn:nbn:de:0030-drops-59680},
  doi =		{10.4230/LIPIcs.FSCD.2016.1},
  annote =	{Keywords: verified compilation; compositional compiler correctness, multi-language semantics, typed low-level languages}
}
Document
DOI: 10.4230/LIPIcs.SNAPL.2015.15
Verified Compilers for a Multi-Language World

Authors: Amal Ahmed

Published in: LIPIcs, Volume 32, 1st Summit on Advances in Programming Languages (SNAPL 2015)

Abstract
Though there has been remarkable progress on formally verified compilers in recent years, most of these compilers suffer from a serious limitation: they are proved correct under the assumption that they will only be used to compile whole programs. This is an unrealistic assumption since most software systems today are comprised of components written in different languages - both typed and untyped - compiled by different compilers to a common target, as well as low-level libraries that may be handwritten in the target language. We are pursuing a new methodology for building verified compilers for today's world of multi-language software. The project has two central themes, both of which stem from a view of compiler correctness as a language interoperability problem. First, to specify correctness of component compilation, we require that if a source component s compiles to target component t, then t linked with some arbitrary target code t' should behave the same as s interoperating with t'. The latter demands a formal semantics of interoperability between the source and target languages. Second, to enable safe interoperability between components compiled from languages as different as ML, Rust, Python, and C, we plan to design a gradually type-safe target language based on LLVM that supports safe interoperability between more precisely typed, less precisely typed, and type-unsafe components. Our approach opens up a new avenue for exploring sensible language interoperability while also tackling compiler correctness.
Cite as

Amal Ahmed. Verified Compilers for a Multi-Language World. In 1st Summit on Advances in Programming Languages (SNAPL 2015). Leibniz International Proceedings in Informatics (LIPIcs), Volume 32, pp. 15-31, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2015)

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@InProceedings{ahmed:LIPIcs.SNAPL.2015.15,
  author =	{Ahmed, Amal},
  title =	{{Verified Compilers for a Multi-Language World}},
  booktitle =	{1st Summit on Advances in Programming Languages (SNAPL 2015)},
  pages =	{15--31},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-939897-80-4},
  ISSN =	{1868-8969},
  year =	{2015},
  volume =	{32},
  editor =	{Ball, Thomas and Bodík, Rastislav and Krishnamurthi, Shriram and Lerner, Benjamin S. and Morriset, Greg},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.SNAPL.2015.15},
  URN =		{urn:nbn:de:0030-drops-50131},
  doi =		{10.4230/LIPIcs.SNAPL.2015.15},
  annote =	{Keywords: verified compilation, compositional compiler correctness, multi-language semantics, typed low-level languages, gradual typing}
}
Document
DOI: 10.4230/DagSemProc.10351.1
10351 Abstracts Collection – Modelling, Controlling and Reasoning About State

Authors: Amal Ahmed, Nick Benton, Lars Birkedal, and Martin Hofmann

Published in: Dagstuhl Seminar Proceedings, Volume 10351, Modelling, Controlling and Reasoning About State (2010)

Abstract
From 29 August 2010 to 3 September 2010, the Dagstuhl Seminar 10351 ``Modelling, Controlling and Reasoning About State '' was held in Schloss Dagstuhl~--~Leibniz Center for Informatics. During the seminar, several participants presented their current research, and ongoing work and open problems were discussed. Abstracts of the presentations given during the seminar as well as abstracts of seminar results and ideas are put together in this paper. Links to extended abstracts or full papers are provided, if available.
Cite as

Amal Ahmed, Nick Benton, Lars Birkedal, and Martin Hofmann. 10351 Abstracts Collection – Modelling, Controlling and Reasoning About State. In Modelling, Controlling and Reasoning About State. Dagstuhl Seminar Proceedings, Volume 10351, pp. 1-16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2010)

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@InProceedings{ahmed_et_al:DagSemProc.10351.1,
  author =	{Ahmed, Amal and Benton, Nick and Birkedal, Lars and Hofmann, Martin},
  title =	{{10351 Abstracts Collection – Modelling, Controlling and Reasoning About State}},
  booktitle =	{Modelling, Controlling and Reasoning About State},
  pages =	{1--16},
  series =	{Dagstuhl Seminar Proceedings (DagSemProc)},
  ISSN =	{1862-4405},
  year =	{2010},
  volume =	{10351},
  editor =	{Amal Ahmed and Nick Benton and Lars Birkedal and Martin Hofmann},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/DagSemProc.10351.1},
  URN =		{urn:nbn:de:0030-drops-28116},
  doi =		{10.4230/DagSemProc.10351.1},
  annote =	{Keywords: Mutable State, Program Logics, Semantics, Type Systems, Verification}
}
Document
DOI: 10.4230/DagSemProc.10351.2
10351 Executive Summary – Modelling, Controlling and Reasoning About State

Authors: Amal Ahmed, Nick Benton, Lars Birkedal, and Martin Hofmann

Published in: Dagstuhl Seminar Proceedings, Volume 10351, Modelling, Controlling and Reasoning About State (2010)

Abstract
From 29 August 2010 to 3 September 2010, the Dagstuhl Seminar 10351 ``Modelling, Controlling and Reasoning About State '' was held in Schloss Dagstuhl~--~Leibniz Center for Informatics. 44 researchers, with interests and expertise in many different aspects of modelling and reasoning about mutable state, met to present their current work and discuss ongoing projects and open problems. This executive summary provides a general overview of the goals of the seminar and of the topics discussed.
Cite as

Amal Ahmed, Nick Benton, Lars Birkedal, and Martin Hofmann. 10351 Executive Summary – Modelling, Controlling and Reasoning About State. In Modelling, Controlling and Reasoning About State. Dagstuhl Seminar Proceedings, Volume 10351, pp. 1-4, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2010)

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@InProceedings{ahmed_et_al:DagSemProc.10351.2,
  author =	{Ahmed, Amal and Benton, Nick and Birkedal, Lars and Hofmann, Martin},
  title =	{{10351 Executive Summary – Modelling, Controlling and Reasoning About State}},
  booktitle =	{Modelling, Controlling and Reasoning About State},
  pages =	{1--4},
  series =	{Dagstuhl Seminar Proceedings (DagSemProc)},
  ISSN =	{1862-4405},
  year =	{2010},
  volume =	{10351},
  editor =	{Amal Ahmed and Nick Benton and Lars Birkedal and Martin Hofmann},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/DagSemProc.10351.2},
  URN =		{urn:nbn:de:0030-drops-28108},
  doi =		{10.4230/DagSemProc.10351.2},
  annote =	{Keywords: Mutable State, Program Logics, Semantics, Type Systems, Verification}
}
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