It's different in practice because languages have built-in "opinions" (often codified by syntax, or the standard library, or other ways) that heavily influence

It's different in practice because languages have built-in "opinions" (often codified by syntax, or the standard library, or other ways) that heavily influence their ecosystem. Functional javascript, or python, is not awesome because the default datastructures are mutable, and the ecosystem of libraries are written in an OOP style using mutable data structures. There is some small value in writing the code you control in as FP a way as possible, but you aren't going to have a ton of success in that unless you are willing to rewrite your dependencies to also be more functional. ReactJS may be a killer app that can influence javascript's "opinions" at the ecosystem scale, but that is going to take more time. I've been using ReactJS since it came out as tech lead on small teams, and it was not without challenges to get an OOP trained team to use React well, and to avoid the OO parts of React. Edit: In theory, yes, if you could somehow statically enforce that your C code (and dependencies, including the OS) have no side effects, then some hypothetical compiler could combine your imperative C statements into functional expressions, though I don't know what advantage that would give you. Maybe I have misunderstood your post.