Programmation purement fonctionnelle

En informatique, la programmation purement fonctionnelle est un paradigme de programmation qui considère toutes les opérations comme l'évaluation de fonctions mathématiques. L'état et les objets immuables sont généralement modélisés à l'aide d'une logique temporelle, en tant que variables explicites représentant l'état du programme à chaque étape de son exécution : l'état d'une variable est transmis en tant que paramètre d'entrée d'une fonction de transformation d'état, qui renvoie l'état mis à jour en tant que partie de sa valeur de retour. Ce style gère les modifications d'état sans perdre la transparence référentielle des expressions du programme. La programmation fonctionnelle pure consiste à s'assurer que les fonctions dans un paradigme fonctionnel, ne dépendent que de leurs arguments, indépendamment de tout état global ou local. Un sous-programme fonctionnel pur ne peut voir que les changements d'état des variables incluses dans sa portée. Différence entre la programmat

Scaling Language Features for Program Verification

Georg Stefan Schmid

Formal verification of real-world software systems remains challenging for a number of reasons, including lack of automation, friction in specifying properties, and limited support for the diverse programming paradigms used in industry. In this thesis we make progress towards a better verification experience in general-purpose programming languages by contributing improvements both to the automated checking and the specification of safety properties in languages combining functional and imperative features. We present our extensions in two parts -- reasoning about shared mutable data, and types as specifications -- both of which ultimately rely on reductions of expressive surface languages to a functional core. Throughout, we instantiate our techniques for the particular example of Scala, a mixed-paradigm language widely-used in industry.The first part shows how to extend a verifier for higher-order functions and immutable data to support imperative programs with shared mutable data. We build upon Stainless, a contract-based verification system that relies on SMT solvers to automatically verify a large fragment of Scala. Our technique extends Stainless to check general heap-manipulating programs against modular specifications in the style of dynamic frames. A novelty of our approach is the translation of imperative function contracts that encodes frame conditions using quantifier-free formulas in first-order logic, instead of relying on quantifiers or on dedicated separation logic reasoning. Our quantifier-free encoding enables SMT solvers to both prove safety and to report counterexamples relative to the semantics of procedure contracts.In the second part we turn to types and type-level programming as an alternative means of specifying correctness properties. While dependent types have been studied extensively for purely-functional languages, we investigate their applications to languages with subtyping and (abstractions of) imperative features. We first study a calculus that provides type-level computation through singleton types and allows abstraction of state and IO through a non-deterministic choice operator. This allows for modelling interactions with existing imprecisely-typed and impure code. Our calculus is formalized and mechanically proven correct using the Coq proof assistant. In addition, we develop a prototypical implementation in the Scala compiler and study typical type-level programming use cases in the Scala ecosystem.

EPFL2022

Programming language abstractions for mobile code

Stéphane Micheloud

Scala is a general-purpose programming language developed at EPFL. It combines the most important concepts found in object-oriented and functional languages. Scala is a statically typed language; in particular it features an advanced type system and supports local type inference. Furthermore it integrates well with the Java and .net platforms: their libraries are accessible without glue code and the Scala compiler generates code for both execution environments. The Scala programming language has several features that make it desirable as a language for distributed application programming. In particular, it supports first-class functions which are useful in relation with the notions of distributed scope and code mobility. In that context, the missing support for run-time types is one important drawback of the Java run-time environment as a target platform. This thesis focuses on the realisation of a new concept combining essential notions from the functional and distributed programming and implying the extension of the notion of lexical scoping to the distributed context. In short, we claim that the notion of lambda abstraction provides an elegant way for dealing with the dynamic rebinding of local references in a distributed execution environment. The key ideas exposed in this research work have been implemented in our Scala compiler. This helped us to evaluate the used techniques, in particular their impact on the reliability and the performance of distributed programs. So far, most research works related to the present subject have focused on functional programming languages, in particular on the ML language family.

EPFL2009

A generic algorithm for checking exhaustivity of pattern matching

Fengyun Liu

Algebraic data types and pattern matching are key features of functional programming languages. Exhaustivity checking of pattern matching is a safety belt that defends against unmatched exceptions at runtime and boosts type safety. However, the presence of language features like inheritance, typecase, traits, GADTs, path-dependent types and union types makes the checking difficult and the algorithm complex. In this paper we propose a generic algorithm that decouples the checking algorithm from specific type theories. The decoupling makes the algorithm simple and enables easy customization for specific type systems.

2016

Scaling Language Features for Program Verification

Georg Stefan Schmid

EPFL2022