Package managers are legion. Every programming language and operating system has its own solution, each with subtly different semantics for dependency resolution. This fragmentation prevents multilingual projects from expressing precise dependencies across language ecosystems; it leaves external system dependencies implicit and unversioned; and it obscures the full dependency graph that supply-chain analysis depends on. We present the Package Calculus, a formalism for dependency resolution that unifies the core semantics of package managers. Through a series of formal reductions, we show how this core is expressive enough to model the diversity of real-world dependency expression languages. The calculus provides the theoretical foundation for future cross-ecosystem tooling, as a lingua franca of dependency expression.

Docker is a developer tool used by millions of developers to build, share and run software stacks. The Docker Desktop clients for Mac and Windows have long used a novel combination of virtualisation and OCaml unikernels to seamlessly run Linux containers on these non-Linux hosts. We reflect on a decade of shipping this functional OCaml code into production across hundreds of millions of developer desktops, and discuss the lessons learnt from our experiences in integrating OCaml deeply into the container architecture that now drives much of the global cloud. We conclude by observing just how good a fit for systems programming that the unikernel approach has been, particularly when combined with the OCaml module and type system.

We present unikernels, a new approach to deploying cloud services via applications written in high-level source code. Unikernels are single-purpose appliances that are compile-time specialised into standalone kernels, and sealed against modification when deployed to a cloud platform. In return they offer significant reduction in image sizes, improved efficiency and security, and should reduce operational costs. Our Mirage prototype compiles OCaml code into unikernels that run on commodity clouds and offer an order of magnitude reduction in code size without significant performance penalty. The architecture combines static type-safety with a single address-space layout that can be made immutable via a hypervisor extension. Mirage contributes a suite of type-safe protocol libraries, and our results demonstrate that the hypervisor is a platform that overcomes the hardware compatibility issues that have made past library operating systems impractical to deploy in the real-world.

We present a case-study of using OCaml within a large product development project, focussing on both the technical and non-technical issues that arose as a result. We draw comparisons between the OCaml team and the other teams that worked on the project, providing comparative data on hiring patterns and cross-team code contribution.

We describe in this paper our implementation of the Xenstored service which is part of the Xen architecture. Xenstored maintains a hierarchical and transactional database, used for storing and managing configuration values.