A multiparty session formalises a set of concurrent communicating participants. The possibility for a participant to delegate some interactions to another participant is crucial for the expressivity of multiparty sessions. We propose the first type system for multiparty sessions with delegation where some communications between participants can be ignored. This allows us to type some sessions with global types representing interesting protocols, which have no type in the standard type systems. Our type system enjoys Subject Reduction, Session Fidelity and partial Lock-freedom. The last property ensures the absence of locks for participants with non-ignored communications. A sound and complete type inference algorithm is also discussed.

Abstract In the ever-evolving landscape of scientific computing, properly supporting the modularity and complexity of modern scientific applications requires new approaches to workflow execution, like seamless interoperability between different workflow systems, distributed-by-design workflow models, and automatic optimisation of data movements. In order to address this need, this article introduces SWIRL, an intermediate representation language for scientific workflows. In contrast with other product-agnostic workflow languages, SWIRL is not designed for human interaction but to serve as a low-level compilation target for distributed workflow execution plans. The main advantages of SWIRL semantics are low-level primitives based on the send/receive programming model and a formal framework ensuring the consistency of the semantics and the specification of translating workflow models represented by Directed Acyclic Graphs (DAGs) into SWIRL workflow descriptions. Additionally, SWIRL offers rewriting rules designed to optimise execution traces, accompanied by corresponding equivalence. An open-source SWIRL compiler toolchain has been developed using the ANTLR Python3 bindings.

We present FJ&λ⋆, a new core calculus that extends Featherweight Java (FJ) with interfaces, λ-expressions, intersection types and a form of dynamic type. Intersection types can be used anywhere, in particular to specify target types of λ-expressions. The dynamic type is exploited to specify parts of the class tables and programs we want to exclude temporarily from static typing. Our main result is the gradual guarantee, which says that if a program is well typed in a class table, then replacing type annotations (from the program and from the class table) with the dynamic type always produces a program that is still well typed in the obtained class table. Furthermore, if a typed program evaluates to a value in a class table, then replacing type annotations with dynamic types always produces a program that evaluates to the same value in the obtained class table.

Abstract We propose a general proof technique to show that a predicate is sound, that is, prevents stuck computation, with respect to a big-step semantics. This result may look surprising, since in big-step semantics there is no difference between non-terminating and stuck computations, hence soundness cannot even be expressed. The key idea is to define constructions yielding an extended version of a given arbitrary big-step semantics, where the difference is made explicit. The extended semantics are exploited in the meta-theory, notably they are necessary to show that the proof technique works. However, they remain transparent when using the proof technique, since it consists in checking three conditions on the original rules only, as we illustrate by several examples.

Intersection types have come a long way since their introduction in the Seventies. They have been exploited for characterising behaviours of λ-terms and π-calculus processes, building λ-models, verifying properties of higher-order programs, synthesising code, and enriching the expressivity of programming languages. This paper is a light overview of intersection types and some of their applications.

We discuss Magda ten years after its design. Magda is a mixin-oriented programming language and its goal is to improve code modularity and, as a consequence, code reuse. The aim of this paper is to survey Magda and position it in today’s programming language scenarios.

We present FJ&$\lambda$, a new core calculus that extends Featherweight Java (FJ) with interfaces, supporting multiple inheritance in a restricted form, $\lambda$-expressions, and intersection types. Our main goal is to formalise how lambdas and intersection types are grafted on Java 8, by studying their properties in a formal setting. We show how intersection types play a significant role in several cases, in particular in the typecast of a $\lambda$-expression and in the typing of conditional expressions. We also embody interface \emph{default methods} in FJ&$\lambda$, since they increase the dynamism of $\lambda$-expressions, by allowing these methods to be called on $\lambda$-expressions. The crucial point in Java 8 and in our calculus is that $\lambda$-expressions can have various types according to the context requirements (target types): indeed, Java code does not compile when $\lambda$-expressions come without target types. In particular, in the operational semantics we must record target types by decorating $\lambda$-expressions, otherwise they would be lost in the runtime expressions. We prove the subject reduction property and progress for the resulting calculus, and we give a type inference algorithm that returns the type of a given program if it is well typed. The design of FJ&$\lambda$ has been driven by the aim of making it a subset of Java 8, while preserving the elegance and compactness of FJ. Indeed, FJ&$\lambda$ programs are typed and behave the same as Java programs.

In this paper we present a novel approach to big-step operational semantics. This approach stems from the observation that the typical type soundness property formulated via a big-step operational semantics is weak, while the option of using a small-

Finding typed encodings of object-oriented into procedural or functional programming sheds light on the theoretical foundations of object-oriented languages and their specific typing constructs and techniques. This article describes a type preserving and computationally adequate interpretation of a full-fledged object calculus that supports message passing and constructs for object update and extension. The target theory is a higher-order λ-calculus with records and recursive folds/unfolds, polymorphic and recursive types, and subtyping. The interpretation specializes to calculi of nonextensible objects, and validates the expected subtypin

We extend the type system for the Lambda Calculus of Objects [16] with a mechanism of width subtyping and a treatment of incomplete objects. The main novelties over previous work are the use of subtype-bounded quantification to capture a new and more direct rendering of MyType polymorphism, and a uniform treatment for other features that were accounted for via different systems in subsequent extensions [7, 6] of [16]. The new system provides for (i) appropriate type specialization of inherited methods, (ii) static detection of errors, (iii) width subtyping compatible with object extension, and (iv) sound typing for partially specified objects.