SBTB 2019: Paul Chiusano, Unison, and why the codebase of the future is a purely functional...

ai.bythebay.io Nov 2025, Oakland, full-stack AI conference Title: Unison, and why the codebase of the future is a purely functional data structure Unison is an open source functional programming language with special support for building distributed, elastic systems. It began as an experiment: rethink all aspects of the programming experience, including the core language, runtime, tooling, as well as code versioning and publishing, and then do whatever is necessary to eliminate needless complexity and make building software once again delightful, or at the very least, reasonable. This talk zooms in on one aspect of Unison: it models the codebase not as a mutable bag of text files, but as a purely functional data structure. We'll explain what that means and show the benefits of the approach, which include: * Perfect incremental compilation and testing, with the compilation and test result caches shared among all collaborators * Refactoring of any size as a totally controlled experience where the codebase always typechecks and the code is always runnable * Instant, 100% accurate renames that never break downstream libraries or users * The ability to assign multiple names to the same definition, with all namings being fully compatible with one another * Simplified and more flexible dependency management; many causes of dependency hell simply cannot arise * The ability to serialize arbitrary Unison code, simply, without dependency management issues * And lots more... Besides introducing the big ideas and theory, we'll also show how the ideas get used in practice by demoing the Unison codebase editing tool live during the talk. It should be a lot of fun!