2,905 research outputs found
A Tree Logic with Graded Paths and Nominals
Regular tree grammars and regular path expressions constitute core constructs
widely used in programming languages and type systems. Nevertheless, there has
been little research so far on reasoning frameworks for path expressions where
node cardinality constraints occur along a path in a tree. We present a logic
capable of expressing deep counting along paths which may include arbitrary
recursive forward and backward navigation. The counting extensions can be seen
as a generalization of graded modalities that count immediate successor nodes.
While the combination of graded modalities, nominals, and inverse modalities
yields undecidable logics over graphs, we show that these features can be
combined in a tree logic decidable in exponential time
Expressive Logical Combinators for Free
International audienceA popular technique for the analysis of web query languages relies on the translation of queries into logical formulas. These formulas are then solved for satisfiability using an off-the-shelf satisfiabil-ity solver. A critical aspect in this approach is the size of the obtained logical formula, since it constitutes a factor that affects the combined complexity of the global approach. We present logical combi-nators whose benefit is to provide an exponential gain in succinctness in terms of the size of the logical representation. This opens the way for solving a wide range of problems such as satisfiability and containment for expressive query languages in exponential-time, even though their direct formulation into the underlying logic results in an exponential blowup of the formula size, yielding an incorrectly presumed two-exponential time complexity. We illustrate this from a practical point of view on a few examples such as numerical occurrence constraints and tree frontier properties which are concrete problems found with semi-structured data
De la KAM avec un Processus d'Ordre Supérieur
National audienceNous présentons un encodage simple et direct de la machine abstraite de Krivine (KAM) dans le calcul de processus d'ordre supérieur HOcore, en utilisant un nombre très restreint de canaux de communication. Cet encodage montre qu'il est possible de capturer l'expressivité du lambda-calcul en HOcore dès que l'on fixe l'ordre d'évaluation. Nous donnons également une nouvelle borne inférieure pour le nombre minimal de restrictions nécessaire pour rendre l'équivalence de programmes dans HOcore indécidable
Howe's Method for Contextual Semantics
International audienceWe show how to use Howe's method to prove that context bisimilarity is a congruence for process calculi equipped with their usual semantics. We apply the method to two extensions of HOĎ€, with passivation and with join patterns, illustrating different proof techniques
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Deriving Abstract Interpreters from Skeletal Semantics
This paper describes a methodology for defining an executable abstract
interpreter from a formal description of the semantics of a programming
language. Our approach is based on Skeletal Semantics and an abstract
interpretation of its semantic meta-language. The correctness of the derived
abstract interpretation can be established by compositionality provided that
correctness properties of the core language-specific constructs are
established. We illustrate the genericness of our method by defining a Value
Analysis for a small imperative language based on its skeletal semantics.Comment: In Proceedings EXPRESS/SOS2023, arXiv:2309.0578
Characterizing contextual equivalence in calculi with passivation
AbstractWe study the problem of characterizing contextual equivalence in higher-order languages with passivation. To overcome the difficulties arising in the proof of congruence of candidate bisimilarities, we introduce a new form of labeled transition semantics together with its associated notion of bisimulation, which we call complementary semantics. Complementary semantics allows to apply the well-known Howeʼs method for proving the congruence of bisimilarities in a higher-order setting, even in the presence of an early form of bisimulation. We use complementary semantics to provide a coinductive characterization of contextual equivalence in the HOπP calculus, an extension of the higher-order π-calculus with passivation, obtaining the first result of this kind. We then study the problem of defining a more effective variant of bisimilarity that still characterizes contextual equivalence, along the lines of Sangiorgiʼs notion of normal bisimilarity. We provide partial results on this difficult problem: we show that a large class of test processes cannot be used to derive a normal bisimilarity in HOπP, but we show that a form of normal bisimilarity can be defined for HOπP without restriction
Non-Deterministic Abstract Machines
We present a generic design of abstract machines for non-deterministic programming languages, such as process calculi or concurrent lambda calculi, that provides a simple way to implement them. Such a machine traverses a term in the search for a redex, making non-deterministic choices when several paths are possible and backtracking when it reaches a dead end, i.e., an irreducible subterm. The search is guaranteed to terminate thanks to term annotations the machine introduces along the way.
We show how to automatically derive a non-deterministic abstract machine from a zipper semantics - a form of structural operational semantics in which the decomposition process of a term into a context and a redex is made explicit. The derivation method ensures the soundness and completeness of the machines w.r.t. the zipper semantics
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