Lambda: The Ultimate Sublanguage (experience report)

We describe our experience teaching an advanced typed functional programming course based around the use of System Fω as a programming language.</jats:p

Knit&Frog: Pattern matching compilation for custom memory representations

Initially present only in functional languages such as OCaml and Haskell, Algebraic Data Types have now become pervasive in mainstream languages, providing nice data abstractions and an elegant way to express functions though pattern-matching. Numerous approaches have been designed to compile rich pattern matching to cleverly designed, ecient decision trees. However, these approaches are specic to a choice of internal memory representation which must accommodate garbage-collection and polymorphism. ADTs now appear in languages more liberal in their memory representation such as Rust. Notably, Rust is now introducing more and more optimizations of the memory layout of Algebraic Data Types. As memory representation and compilation are interdependent, it raises the question of pattern matching compilation in the presence of non-regular, potentially customized, memory layouts. In this report, we present Knit&Frog, a framework to compile pattern-matching for monomorphic ADTs, parametrized by an arbitrary memory representation. We propose a novel way to describe choices of memory representation along with a validity condition under which we prove the correctness of our compilation scheme. The approach is implemented in a prototype tool ribbit.Initialement présents dans les langages fonctionnels comme Ocaml et Haskell, les types algébriques sont maintenant de plus en plus présents dans les langages mainstream comme Rust. Ils permettent une abstraction commode des données et une façon élégante de décrire des fonctions via le fitrage de motifs (pattern-matching). Ce rapport de recherche présente Knit&Frog, un cadre formel pour décrire des représentations mémoires de types algébrique paramétré par la représentation mémoire. La correction de l'algorithme est prouvée sous une hypothèse de validité de la représentation. L'algorithme est implémenté dans l'outil ribbit. Le principal avantage de l'approche est l'indépendance de l'algorithme et de sa représentation mémoire,qui permettra à terme de décrire des représentations optimisées sans perdre de l'expressivité

Towards A Practical High-Assurance Systems Programming Language

Writing correct and performant low-level systems code is a notoriously demanding job, even for experienced developers. To make the matter worse, formally reasoning about their correctness properties introduces yet another level of complexity to the task. It requires considerable expertise in both systems programming and formal verification. The development can be extremely costly due to the sheer complexity of the systems and the nuances in them, if not assisted with appropriate tools that provide abstraction and automation. Cogent is designed to alleviate the burden on developers when writing and verifying systems code. It is a high-level functional language with a certifying compiler, which automatically proves the correctness of the compiled code and also provides a purely functional abstraction of the low-level program to the developer. Equational reasoning techniques can then be used to prove functional correctness properties of the program on top of this abstract semantics, which is notably less laborious than directly verifying the C code. To make Cogent a more approachable and effective tool for developing real-world systems, we further strengthen the framework by extending the core language and its ecosystem. Specifically, we enrich the language to allow users to control the memory representation of algebraic data types, while retaining the automatic proof with a data layout refinement calculus. We repurpose existing tools in a novel way and develop an intuitive foreign function interface, which provides users a seamless experience when using Cogent in conjunction with native C. We augment the Cogent ecosystem with a property-based testing framework, which helps developers better understand the impact formal verification has on their programs and enables a progressive approach to producing high-assurance systems. Finally we explore refinement type systems, which we plan to incorporate into Cogent for more expressiveness and better integration of systems programmers with the verification process

Fundamental Approaches to Software Engineering

computer software maintenance; computer software selection and evaluation; formal logic; formal methods; formal specification; programming languages; semantics; software engineering; specifications; verificatio

Fundamental Approaches to Software Engineering

This open access book constitutes the proceedings of the 24th International Conference on Fundamental Approaches to Software Engineering, FASE 2021, which took place during March 27–April 1, 2021, and was held as part of the Joint Conferences on Theory and Practice of Software, ETAPS 2021. The conference was planned to take place in Luxembourg but changed to an online format due to the COVID-19 pandemic. The 16 full papers presented in this volume were carefully reviewed and selected from 52 submissions. The book also contains 4 Test-Comp contributions