I completely agree, but I still question the purpose of FP languages. Writing the S3 upload code is quite hard, if you really want to handle all possible error scenarios. Even if you use whatever library for that, you still need to know about which errors can it trigger and which need to be handle, and how to handle them. The mental work can be equal to the core function for generating the file. In any language, I'd separate these two pieces of code, but I'm not sure if I'd want to handle S3 upload logic with all the error handling in a FP language. That said, I've not used Clojure yet and that seems like a very pragmatic language, which might be actually usable even for these parts of the code.