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clojureleiningen

Clojure map runs in cider, but not lein run

I'm having an issue where my project runs in Cider, but not with lein run.

Consider these functions in core.clj:

(def my-vec ["a" "b" "c"])

(defn dostuff [x] (spit "/home/dirty/file.txt" x :append true))

(defn -main [& args] (map dostuff my-vec))

Now, when I open Cider repl and enter (-main), this will run and file.txt will contain "abc...". However, if I go to the project with the terminal and run lein run it runs for a few moments and then shuts down. But file.txt is not written to. What am I overlooking?

Solution

  • map is a lazy sequence, it's not meant for side effects. If you want to force the realization of the lazy sequence, you need to wrap your map in a doall. You shouldn't be using map for this in the first place as you don't care about the resulting sequence. See doseq:

    (doseq [x my-vec] (dostuff x))