In practice all the interop lives at the edges of the application. As a concrete example, Pedestal HTTP server has around 18,000 lines of code, and 96% of it is

In practice all the interop lives at the edges of the application. As a concrete example, Pedestal HTTP server has around 18,000 lines of code, and 96% of it is pure functions. All the IO and side effects are encapsulated in the remaining 4% of the code. This has been a common scenario for the vast majority of Clojure programs I've worked on in the past decade. https://www.youtube.com/watch?v=0if71HOyVjY https://www.youtube.com/watch?v=0if71HOyVjY Core of the application does data transformations using native Clojure data structures. This is where all your interesting business logic lives. The interop lives at the edges and typically used for stuff like database drivers, HTTP servers, file access, and so on.