The widespread adoption of Free and Open Source Software (FOSS) in many strategic contexts of the information technology society has drawn the attention on the issues regarding how to handle the complexity of assembling and managing a huge number of (packaged) components in a consistent and effective way. FOSS distributions (and in particular GNU/Linux-based ones) have always provided tools for managing the tasks of installing, removing and upgrading the (packaged) components they were made of. While these tools provide a (not always effective) way to handle these tasks on the client side, there is still a lack of tools that could help the distribution editors to maintain, on the server side, large and high-quality distributions. In this paper we present our research whose main goal is to fill this gap: we show our approach, the tools we have developed and their application with experimental results. Our contribution provides an effective and automatic way to support distribution editors in handling those issues that were, until now, mostly addressed using ad-hoc tools and manual techniques.

We propose regular expression types as a foundation for statically typed XML processing languages. Regular expression types, like most schema languages for XML, introduce regular expression notations such as repetition (*), alternation (|), etc., to describe XML documents. The novelty of our type system is a semantic presentation of subtyping, as inclusion between the sets of documents denoted by two types. We give several examples illustrating the usefulness of this form of subtyping in XML processing.The decision problem for the subtype relation reduces to the inclusion problem between tree automata, which is known to be exptime-complete. To avoid this high complexity in typical cases, we develop a practical algorithm that, unlike classical algorithms based on determinization of tree automata, checks the inclusion relation by a top-down traversal of the original type expressions. The main advantage of this algorithm is that it can exploit the property that type expressions being compared often share portions of their representations. Our algorithm is a variant of Aiken and Murphy's set-inclusion constraint solver, to which are added several new implementation techniques, correctness proofs, and preliminary performance measurements on some small programs in the domain of typed XML processing.

We propose regular expression types as a foundation for statically typed XML processing languages. Regular expression types, like most schema languages for XML, introduce regular expression notations such as repetition (*), alternation (|), etc., to describe XML documents. The novelty of our type system is a semantic presentation of subtyping, as inclusion between the sets of documents denoted by two types. We give several examples illustrating the usefulness of this form of subtyping in XML processing.The decision problem for the subtype relation reduces to the inclusion problem between tree automata, which is known to be exptime-complete. To avoid this high complexity in typical cases, we develop a practical algorithm that, unlike classical algorithms based on determinization of tree automata, checks the inclusion relation by a top-down traversal of the original type expressions. The main advantage of this algorithm is that it can exploit the property that type expressions being compared often share portions of their representations. Our algorithm is a variant of Aiken and Murphy's set-inclusion constraint solver, to which are added several new implementation techniques, correctness proofs, and preliminary performance measurements on some small programs in the domain of typed XML processing.

We present a model of recursive and impredicatively quantified types with mutable references. We interpret in this model all of the type constructors needed for typed intermediate languages and typed assembly languages used for object-oriented and functional languages. We establish in this purely semantic fashion a soundness proof of the typing systems underlying these TILs and TALs-ensuring that every well-typed program is safe. The technique is generic, and applies to any small-step semantics including λ-calculus, labeled transition systems, and von Neumann machines. It is also simple, and reduces mainly to defining a Kripke semantics of the Gödel-Löb logic of provability. We have mechanically verified in Coq the soundness of our type system as applied to a von Neumann machine.

Objective ML is a small practical extension to ML with objects and top level classes. It is fully compatible with ML; its type system is based on ML polymorphism, record types with polymorphic access, and a better treatment of type abbreviations. Objective ML allows for most features of object‐oriented languages including multiple inheritance, methods returning self and binary methods as well as parametric classes. This demonstrates that objects can be added to strongly typed languages based on ML polymorphism. © 1998 John Wiley & Sons, Inc.

International audienceWe present a model of recursive and impredicatively quantified types with mutable references. We interpret in this model all of the type constructors needed for typed intermediate languages and typed assembly languages used for object-oriented and functional languages. We establish in this purely semantic fashion a soundness proof of the typing systems underlying these TILs and TALs---ensuring that every well-typed program is safe. The technique is generic, and applies to any small-step semantics including λ-calculus, labeled transition systems, and von Neumann machines. It is also simple, and reduces mainly to defining a Kripke semantics of the Gödel-Löb logic of provability. We have mechanically verified in Coq the soundness of our type system as applied to a von Neumann machine

Tierless Web programming languages allow programmers to combine client-side and server-side programming in a single program. Programmers can then define components with both client and server parts and get flexible, efficient and typesafe client-server communications. However, the expressive client-server features found in most tierless languages are not necessarily compatible with functionalities found in many mainstream languages. In particular, we would like to benefit from type safety, an efficient execution, static compilation, modularity and separate compilation.In this paper, we propose E , an industrial-strength tierless functional Web programming language which extends OC with support for rich client/server interactions. It allows to build whole applications as a single distributed program, in which it is possible to define modular tierless libraries with both server and client behaviors and combine them effortlessly. E is the only language that combines type-safe and efficient client/server communications with a static compilation model that supports separate compilation and modularity. It also supports excellent integration with OC , allowing to transparently leverage its ecosystem.To achieve all these features, E borrows ideas not only from distributed programming languages, but also from meta-programming and modern module systems. We present the design of E , how it can be used in practice and its formalization; including its type system, semantics and compilation scheme. We show that this compilation scheme preserves typing and semantics, and that it supports separate compilation.This juggling of many different technologies does not only make programming more complicated, it also imposes strong constraints on code organization and prevents modularity. Let us consider the case where we want to add a comment widget to a website. This widget requires J S code for client interactions, for example a convenient editor. It also requires server code that will store and serve the comments and potentially some associated database queries. This code will thus be split in two codebases and up to three languages. Furthermore, in order to be properly integrated in the larger website, the internal communications between the client and server parts of the widget will be exposed to the rest of the program. All these programming constraints, which stem directly from the way Web programming is done currently, make it impossible to preserve abstraction and encapsulation for widgets who have both client and server aspects. This hinders safety and reusability of widgets by preventing programmers to create selfcontained independent libraries that have both client and server aspects.: A Language for Modular Tierless Web Programming :3programming often relies on numerous external libraries (for encryption, HTML, logging, . . . ). We wanted to leverage all the existing tools and libraries developed either in the O project or the larger OC ecosystem. The design of a Modular Tierless languageTo build such a language with suppo...

International audienceWe construct a realizability model of recursive polymorphic types, starting from an untyped language of terms and contexts. An orthogonality relation e⊥π indicates when a term e and a context π may be safely combined in the language. Types are interpreted as sets of terms closed by biorthogonality. Our main result states that recursive types are approximated by converging sequences of interval types. Our proof is based on a “type-directed” approximation technique, which departs from the “language-directed” approximation technique developed by MacQueen, Plotkin and Sethi in the ideal model. We thus keep the language elementary (a call-by-name λ-calculus) and unstratified (no typecase, no reduction labels). We also include a short account of parametricity, based on an orthogonality relation between quadruples of terms and contexts