Several types of types in programming languages

Types are an important part of any modern programming language, but we often forget that the concept of type we understand nowadays is not the same it was perceived in the sixties. Moreover, we conflate the concept of "type" in programming languages with the concept of the same name in mathematical logic, an identification that is only the result of the convergence of two different paths, which started apart with different aims. The paper will present several remarks (some historical, some of more conceptual character) on the subject, as a basis for a further investigation. The thesis we will argue is that there are three different characters at play in programming languages, all of them now called types: the technical concept used in language design to guide implementation; the general abstraction mechanism used as a modelling tool; the classifying tool inherited from mathematical logic. We will suggest three possible dates ad quem for their presence in the programming language literature, suggesting that the emergence of the concept of type in computer science is relatively independent from the logical tradition, until the Curry-Howard isomorphism will make an explicit bridge between them.Comment: History and Philosophy of Computing, HAPOC 2015. To appear in LNC

From Models to Simulations

This book analyses the impact computerization has had on contemporary science and explains the origins, technical nature and epistemological consequences of the current decisive interplay between technology and science: an intertwining of formalism, computation, data acquisition, data and visualization and how these factors have led to the spread of simulation models since the 1950s. Using historical, comparative and interpretative case studies from a range of disciplines, with a particular emphasis on the case of plant studies, the author shows how and why computers, data treatment devices and programming languages have occasioned a gradual but irresistible and massive shift from mathematical models to computer simulations

TAL Bibliography (1951-2002). Parte I

No abstract availabl

Introduction to the Literature on Semantics

An introduction to the literature on semantics. Included are pointers to the literature on axiomatic semantics, denotational semantics, operational semantics, and type theory

Forecasting Urban Traffic in France, 1950s to 2000s: The Nation-State, private engineering firms and the globalization of an area of expertise

Despite of its impact on urban transportation policies after the World War II, urban travel demand modeling (UTDM) - an array of mathematical tools and practices geared towards predicting flows in urban transportation networks, such as urban highways and mass transit systems - has received scant attention from humanities and social sciences scholars. This working paper offers a first long-term analysis - from the 1950s to the 2000s - of the trajectory of this kind of modeling in France. To do so, it makes use of an analytical framework which envisages modeling practices as a production process: aside from the "product" itself, i.e. the main characteristics of the model under study, the analysis is interested in the different actors involved in producing the model (individuals and institutions), as well as the "raw materials" (for example, data from surveys of household travel) and the "means of production", such as computer facilities (hardware and software), which are necessary for its production and implementation. Based on this analytical framework, this paper highlights a process characterized by two main developments. From 1950-1980, State French engineers along with private consulting firms, after having familiarized themselves with American modeling practices, succeeded in creating a national expertise in this domain, which the central French state normalized, disseminated, and implemented on a large scale throughout the national territory in the 1970s. The post 1980 period clearly contrasts with what went before. Indeed, evidence shows that the French state progressively withdrew from UTDM, and, therefore, prepared the way for the rise to dominance of private (and more often that not foreign) engineering consulting firms, which became the main repositories of expertise concerning urban traffic forecasting in France.En dépit de l'importance de la modélisation des déplacements urbains en matière de politiques de transports, force est de constater la quasi-absence d'intérêt dont les historiens et autres chercheurs en sciences sociales ont fait montre à son égard jusqu'à présent. Ce document propose une première analyse de la modélisation des déplacements urbains en France, des années 1950 au début des années 2010. Pour ce faire, nous avons adopté une perspective particulière, qui envisage la modélisation comme un processus de production : outre le " produit " lui-même (la structure des modèles), nous nous sommes intéressés à la fois aux différents acteurs (individus et institutions) qui ont produit ce type de modélisation, aux " matières premières " (enquêtes sur la mobilité...) et aux " moyens de production " (logiciels et machines informatiques) nécessaires à sa production et sa mise en œuvre. Regardée à travers cette grille d'analyse, la trajectoire de la modélisation des déplacements urbains en France met en évidence deux grandes périodes distinctes, aux caractéristiques contrastées. Après avoir commencé par se familiariser, à partir des années 1950, avec la modélisation américaine, les acteurs français, publics et privés, construisent, sous l'égide de la puissance publique, durant la décennie suivante et le début des années 1970, une expertise nationale que l'Administration centrale va ensuite " normaliser " et diffuser massivement à travers le territoire. Comme pour le cas nord-américain, la période " 1980-présent " est en revanche marquée par la domination progressive de ce champ de modélisation par le secteur privé, représenté souvent par des bureaux d'études étrangers et des entreprises productrices de logiciels originaires de pays autres que la France. Ce sont ces acteurs privés qui deviennent le vecteur principal du changement dans les pratiques en matière de modélisation des déplacements urbains en France après 1980

Constructive Many-One Reduction from the Halting Problem to Semi-Unification

Semi-unification is the combination of first-order unification and first-order matching. The undecidability of semi-unification has been proven by Kfoury, Tiuryn, and Urzyczyn in the 1990s by Turing reduction from Turing machine immortality (existence of a diverging configuration). The particular Turing reduction is intricate, uses non-computational principles, and involves various intermediate models of computation. The present work gives a constructive many-one reduction from the Turing machine halting problem to semi-unification. This establishes RE-completeness of semi-unification under many-one reductions. Computability of the reduction function, constructivity of the argument, and correctness of the argument is witnessed by an axiom-free mechanization in the Coq proof assistant. Arguably, this serves as comprehensive, precise, and surveyable evidence for the result at hand. The mechanization is incorporated into the existing, well-maintained Coq library of undecidability proofs. Notably, a variant of Hooper's argument for the undecidability of Turing machine immortality is part of the mechanization.Comment: CSL 2022 - LMCS special issu