The annual State of Clojure survey has a lot of interesting stats https://clojure.org/news/2022/06/02/state-of-clojure-2022

See also https://clojurians.slack.com/stats for Slack stats.

clojure.edn is the preferred way of storing map data for small files, and storing ns forms and defs in a file to mark state seems like it could go wrong in lots of strange ways. What are you trying to accomplish with this?

I want to save program state periodically, and then give the user the option to load that state when starting

Who are the "users" in this scenario?

me

What program state needs to be saved? Loading ns forms and simple defs is usually fast and doesn't need to be persisted like this. Is there an expensive computation that you need to cache?

expensive computation - yes

I run digital filters on time series data. Startup will take > 15 min with no state loading. I want to reduce startup to a few seconds.

For expensive computation, you can do something like:

(defonce my-result
 (if (.exists ( "my-result.edn"))
    (clojure.edn/read (io/reader "my-result.edn"))
    (let [res (my-expensive-computation)]
      (spit "my-result.edn" (pr-str res))
      res))

That will make sure your expensive computation only happens once and take advantage of the persisted file if it's available.

Oh cool!

That's awesome

One thing to note with defonce -it really only does run once per session, which means that if the inputs to my-expensive-computation have changed, or my-expensive-computation has different implementation details (e.g. your filter parameters have changed), attempting to redefine the my-result var will not recompute your results. So you'll need to make those checks yourself.

You can always get around that by binding a new var, of course - just one thing to watch out for when using this approach.

Yeah, I read up on defonce

This is a slick solution

you can unbind vars whenever you want. in cider the command is ctrl-U

@UFTRLDZEW do I need to import something to get io/reader? When I try just plain io, I get:

No such namespace: io

class java.io.BufferedReader cannot be cast to class java.io.PushbackReader

My bad, I wrote that answer without docs handy and forgot about the type conversion issue here: https://clojuredocs.org/clojure.edn/read

Ugh! Looks like I forgot to update the docs/docstrings in several places when I added that. Sorry. It's listed here https://github.com/clojure/tools.cli/blob/master/src/main/clojure/clojure/tools/cli.cljc#L291-L312 but that's a private function which doesn't appear in the API docs so that's not very helpful. tools.cli really does need some documentation love. I'll try to find some time to work on it "soon" (but, unfortunately, I've stopped using it in all my projects so it's become a lower priority).

I can fork and update the README.md at least. Should I add something to the existing example (with port number, etc.) or just do a new section?

BTW I got my use case to work with :missing perfectly

Contrib libraries do not accept PRs so forking and updating isn't going to get accepted back. I need to write some proper documentation for that library -- it's long overdue!

Ah, gotcha, thanks!

I've updated the README and docstrings for this. I'll be making a minor new release this weekend I expect.