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We present a streamlined theory of session types based on a simple yet general and expressive formalism whose main features are semantically characterized and where each design choice is semantically justified. We formally define the semantics of session types and use it to define the subsessioning relation. We give a coinductive characterization of subsessioning and describe algorithms to decide all the key relations defined in the article. We show that all monomorphic dyadic session types proposed in the literature are particular cases of our session types.

Reversible debugging provides developers with a way to execute their applications both forward and backward, seeking the cause of an unexpected or undesired event. In a concurrent setting, reversing actions in the exact reverse order in which they have been executed may lead to undo many actions that were not related to the bug under analysis. On the other hand, undoing actions in some order that violates causal dependencies may lead to states that could not be reached in a forward execution. We propose an approach based on causal-consistent reversibility: each action can be reversed if all its consequences have already been reversed. The main feature of the approach is that it allows the programmer to easily individuate and undo exactly the actions that caused a given misbehavior till the corresponding bug is reached. This paper major contribution is the individuation of the appropriate primitives for causal-consistent reversible debugging and their prototype implementation in the CaReDeb tool. We also show how to apply CaReDeb to individuate common real-world concurrent bugs.

This paper proposes a global escape mechanism which can handle unexpected or unwanted conditions changing the default execution of distributed communicational flows, preserving compatibility of the multiparty conversations. Our escape is realised by a collection of asynchronous local exceptions which can be thrown at any stage of the communication and to any subsets of participants in a multiparty session. This flexibility enables to model complex exceptions such as criss-crossing global interactions and fault tolerance for distributed cooperating threads. Guided by multiparty session types, our semantics automatically provides an efficient termination algorithm for global escapes with low complexity of exception messages.

Both single and multiple class-based inheritance are often inappropriate as a reuse mechanism, because classes play two competing roles. Namely, a class is both a generator of instances and a unit of reuse. Traits are composable pure units of behavior reuse, consisting only of methods, that have been proposed as an add-on to single class-based inheritance in order to improve reuse. However, adopting traits as an add-on to traditional class-based inheritance is not enough: classes, besides their primary role of generators of instances, still play the competing role of units of reuse. Therefore, a style of programming oriented to reuse is not enforced by the language, but left to the programmer's skills. Traits have been originally proposed in the setting of dynamically typed language. When static typing is also taken into account, the role of unit of reuse and the role of type are competing, too.We argue that, in order to support the development of reusable program components, object oriented programming languages should be designed according to the principle that each software structuring construct must have exactly one role. We propose a realignment of the class-based object-oriented paradigm by presenting programming language features that separate completely the declarations of object type, behavior and generator. We illustrate our proposal through a core calculus and prove the soundness of the type system w.r.t. the operational semantics.

International audienceA recent trend in programming language research is to use behavioral type theory to ensure various correctness properties of largescale, communication-intensive systems. Behavioral types encompass concepts such as interfaces, communication protocols, contracts, and choreography. The successful application of behavioral types requires a solid understanding of several practical aspects, from their representation in a concrete programming language, to their integration with other programming constructs such as methods and functions, to design and monitoring methodologies that take behaviors into account. This survey provides an overview of the state of the art of these aspects, which we summarize as the pragmatics of behavioral types

Session types are a formalism used to model structured communication-based programming. A binary session type describes communication by specifying the type and direction of data exchanged between two parties. When session types and session processes are added to the syntax of standard π -calculus they give rise to additional separate syntactic categories. As a consequence, when new type features are added, there is duplication of effort in the theory: the proofs of properties must be checked both on standard types and on session types. We show that session types are encodable into standard π -types, relying on linear and variant types. Besides being an expressivity result, the encoding (i) removes the above redundancies in the syntax, and (ii) the properties of session types are derived as straightforward corollaries, exploiting the corresponding properties of standard π -types.The robustness of the encoding is tested on a few extensions of session types, including subtyping, polymorphism and higher-order communications.

Abstract. Deadlock detection in concurrent programs that create networks with arbitrary numbers of nodes is extremely complex and solutions either give imprecise answers or do not scale. To enable the analysis of such programs, (1) we define an algorithm for detecting deadlocks of a basic model featuring recursion and fresh name generation: the lam programs, and (2) we design a type system for value passing CCS that returns lam programs. As a byproduct of these two techniques, we have an algorithm that is more powerful than previous ones and that can be easily integrated in the current release of TyPiCal, a type-based analyser for pi-calculus.