We have been developing a distributed application called Lokalisierung using functional programming since 2015. Lokalisierung automatically configures mobiles devices in a large organization of car-inspection shops. It uses peer-to-peer synchronization to distribute configuration data among the devices, without the use of a central server. This paper describes the original design and evolution of the system. Specifically, we highlight how the event-based architecture supports synchronization but also enables flexibility for changes after the original rollout such as undoing configuration changes, and database thinning. We also reflect on design and implementation mistakes we made during its 10-year development.

Mike Sperber is CEO of Active Group, a software consultancy in Tübingen, Germany that develops software for client projects using functional programming. He has a long history of publishing on functional programming, including many research papers, and was the project editor for the R6RS standard for the Scheme programming language. He has also developed an introductory course in programming in use at several German universities, based on the PLT group’s Program by Design approach. He also co-authored (with Nicole Rauch and Lars Hupel) the curriculum on Functional Software Architecture for iSAQB.