> Another project starts up and wants to use the nice UI code. We designate it for a separate library. The first project must isolate and make everything generi

> Another project starts up and wants to use the nice UI code. We designate it for a separate library. The first project must isolate and make everything generic. The requirement is that both projects must work on top of that library and the first one cannot loose any functionality You are in luck! You used clojure and so 90% of your code is already made up of pure functions! And it's easy, with existing tooling, to move those functions to another namespace. Of the remaining 10%, because you aren't running both UIs in the same process, the parts that will cause you problems are the parts that are Project A specific AND critical to the operation of the library. These are usually top level setup functions. These functions, a half dozen for a complex UI, will need manual changes without much tool based refactoring assistance. Luckily because they tend to be setup style functions, existing tests and playing around at the repl will allow you to quickly confirm the refactoring was correct. So in the end even with a complex refactoring like you described you only need to manually worry about maybe 100-200 loc in a 10kloc codebase. And it should take you a lot less time and effort than refactoring the code would if it was in Java.