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Comment by sansnomme | Hacker News Reader

A very important caveat: Clojure compilation is not side-effect free. If you are generating the JVM equivalent of a binary (excluding the assumption of stuff like GraalVM) i.e. a überjar, you are going to have a bad day if your code does stuff like edit configuration files, call a JSON API etc. The code would run during the compilation stage. Something to take note of.

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That's false, building an uberjar has nothing to do wit that. If you're packaging an application typically your -main needs to be AOT compiled, that's why you put :gen-class in your ns declaration. That namespace will get AOT compiled. This still doesn't pose any issues since you shouldn't be doing such side effects in the toplevel. So

    (alter-config-file!)

is bad because that code will run during compilation, but in

    (defn -main [& args]
      (alter-config-file!)
      (app!))

it will run only after calling -main.

Evaluation != Compilation that outputs a binary. This is what happens when language authors become overly obsessed with the elegance of SICP and completely forget how to slay dragons, properly.

I find this comment puzzling, since uberjars are the normal deployment model of Clojure apps and they work well.

Are you referring to a situation where you are developing macros and end up doing something at compile time that should happen at runtime? Or maybe a situation where you put your application logic in statements outside function definitions, possibly copied from a REPL session?

https://stackoverflow.com/questions/31324519/clojure-how-to-...

Oh right, I can see how you might hit this when starting out.

What I did with my first clojure web app is simply leave (main) at the end of the file. This would cause an error telling me that a port is unavailable.

But still Clojure is a lot of fun and that's something you want to look for in a language.

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