UI, Pure and Simple (by Christian Johansen)

Christian Johansen introduces Replicant, a pure, stateless Clojure rendering library that decouples UI from state management.

The London Clojurians are happy to present: ~~~~ reClojure 2025 ~~~ Title: UI, Pure and Simple Speaker: Christian Johansen React introduced the idea that the UI is a function of application state, and it changed the way we think about building UIs. Unfortunately, it also allowed mutable state everywhere. What if UI rendering was truly functional — stateless, deterministic, and built entirely on data? Enter Replicant: a Clojure rendering library with no dependencies and no state management, just immutable data and pure functions. In this talk, we’ll use Replicant to explore how Clojure’s strengths can refine UI development once again. Let's build modular UIs that decouple rendering from state management, are fully testable, and dramatically simpler than the current state of the art. Speaker Bio: I am a software developer at the Norwegian Food Safety Authority where I build systems with Clojure and Datomic. I have 20 years of experience, and have been working full-time with Clojure for the last 10 of those. My career has focused on web tech, and love doing what it takes to ship working software to users: from setting up infrastructure to data modeling and frontend work. I love sharing, and keep a blog (in Norwegian) with my co-workers, give frequent talks at conferences, used to teach courses, and maintain a hodge-podge of open source software libraries in the Clojure ecosystem. Thank you to our sponsors: - juxt.pro/ - flexiana.com/ - freshcodeit.com/ - nubank.com.br/