Generic Programming with Extensible Data Types; Or, Making Ad Hoc Extensible Data Types Less Ad Hoc

We present a novel approach to generic programming over extensible data types. Row types capture the structure of records and variants, and can be used to express record and variant subtyping, record extension, and modular composition of case branches. We extend row typing to capture generic programming over rows themselves, capturing patterns including lifting operations to records and variations from their component types, and the duality between cases blocks over variants and records of labeled functions, without placing specific requirements on the fields or constructors present in the records and variants. We formalize our approach in System R{\omega}, an extension of F{\omega} with row types, and give a denotational semantics for (stratified) R{\omega} in Agda.Comment: To appear at: International Conference on Functional Programming 2023 Corrected citations from previous versio

Implementing an Embedded Compiler using Program Transformation Rules

(To appear)International audienceDomain-specific languages (DSLs) are well-recognized to ease programming and improve robustness for a specific domain, by providing high-level domain-specific notations and verifications of domain-specific properties. The compiler of a DSL, however, is often difficult to develop and maintain, due to the need to define a specific treatment for a large and potentially increasing number of language constructs. To address this issue, we propose an approach for specifying a DSL compiler and verifier using control-flow sensitive concrete-syntax based matching rules. These rules either collect information about the source code to carry out verifications or perform transformations to carry out compilation. Because rules only mention the relevant constructs, using their concrete syntax, and hide the complexity of control-flow graph traversal, it is easy to understand the purpose of each rule. Furthermore, new compilation steps can be added using only a small number of lines of code. We explore this approach in the context of the z2z DSL for network gateway development, and show that the core of its compiler and verifier can be implemented in this manner

The (In)Efficiency of interaction

Evaluating higher-order functional programs through abstract machines inspired by the geometry of the interaction is known to induce space efficiencies, the price being time performances often poorer than those obtainable with traditional, environment-based, abstract machines. Although families of lambda-terms for which the former is exponentially less efficient than the latter do exist, it is currently unknown how general this phenomenon is, and how far the inefficiencies can go, in the worst case. We answer these questions formulating four different well-known abstract machines inside a common definitional framework, this way being able to give sharp results about the relative time efficiencies. We also prove that non-idempotent intersection type theories are able to precisely reflect the time performances of the interactive abstract machine, this way showing that its time-inefficiency ultimately descends from the presence of higher-order types

Sheaf semantics of termination-insensitive noninterference

We propose a new sheaf semantics for secure information flow over a space of abstract behaviors, based on synthetic domain theory: security classes are open/closed partitions, types are sheaves, and redaction of sensitive information corresponds to restricting a sheaf to a closed subspace. Our security-aware computational model satisfies termination-insensitive noninterference automatically, and therefore constitutes an intrinsic alternative to state of the art extrinsic/relational models of noninterference. Our semantics is the latest application of Sterling and Harper's recent re-interpretation of phase distinctions and noninterference in programming languages in terms of Artin gluing and topos-theoretic open/closed modalities. Prior applications include parametricity for ML modules, the proof of normalization for cubical type theory by Sterling and Angiuli, and the cost-aware logical framework of Niu et al. In this paper we employ the phase distinction perspective twice: first to reconstruct the syntax and semantics of secure information flow as a lattice of phase distinctions between "higher" and "lower" security, and second to verify the computational adequacy of our sheaf semantics vis-\`a-vis an extension of Abadi et al.'s dependency core calculus with a construct for declassifying termination channels.Comment: Extended version of FSCD '22 paper with full technical appendice

Programming Languages and Systems

This open access book constitutes the proceedings of the 30th European Symposium on Programming, ESOP 2021, which was held during March 27 until April 1, 2021, as part of the European Joint Conferences on Theory and Practice of Software, ETAPS 2021. The conference was planned to take place in Luxembourg and changed to an online format due to the COVID-19 pandemic. The 24 papers included in this volume were carefully reviewed and selected from 79 submissions. They deal with fundamental issues in the specification, design, analysis, and implementation of programming languages and systems

Reflections of Closures

The idea that programs are data forms the bedrock of functional programming languages, but it is also found in object-oriented languages and recent iterations of systems languages. Since passing and returning programs as data is incompatible with the architecture of modern machines, implementations of such a feature gives rise to closures, which package code with the environment that it needs to run. The first implementations of these objects are as part of the runtime system of an abstract machine. However, to be able to optimize these structures, compiler writers often choose instead to embed this structure in their code when compiling to lower-level languages in a transformation called closure conversion. While this transformation and closures more generally are well studied with respect to certain types of programming languages, how such a language interacts with different evaluation strategies still remains unstudied in a theoretical setting. Moreover, the current approaches to performing, optimizing, and proving correct this transformation lack the flexibility of other language features. This thesis develops these ideas by presenting closure conversions for missing evaluation strategies, specifying a new implementation approach that allows for the flexible implementation and optimization of closures, and formalizing them in an intermediate language that captures multiple notions of closures and evaluation strategies in one. Our approach follows from first principles meaning that our closures are a reflection of the environment-based abstract machines that birth them. We develop an approach to reasoning about closures that connects their equational properties with the abstract machines on which they run. Thereby, we can prove not only that closure conversion does not change the output of programs, but that closure conversion removes the need for the runtime system to capture closures

Automated Deduction – CADE 28

This open access book constitutes the proceeding of the 28th International Conference on Automated Deduction, CADE 28, held virtually in July 2021. The 29 full papers and 7 system descriptions presented together with 2 invited papers were carefully reviewed and selected from 76 submissions. CADE is the major forum for the presentation of research in all aspects of automated deduction, including foundations, applications, implementations, and practical experience. The papers are organized in the following topics: Logical foundations; theory and principles; implementation and application; ATP and AI; and system descriptions

Non-Deterministic Functions as Non-Deterministic Processes (Extended Version)

We study encodings of the lambda-calculus into the pi-calculus in the unexplored case of calculi with non-determinism and failures. On the sequential side, we consider lambdafail, a new non-deterministic calculus in which intersection types control resources (terms); on the concurrent side, we consider spi, a pi-calculus in which non-determinism and failure rest upon a Curry-Howard correspondence between linear logic and session types. We present a typed encoding of lambdafail into spi and establish its correctness. Our encoding precisely explains the interplay of non-deterministic and fail-prone evaluation in lambdafail via typed processes in spi. In particular, it shows how failures in sequential evaluation (absence/excess of resources) can be neatly codified as interaction protocols