Clojurians Log v2

I'm trying to figure out if the variation I see is because of GC or thread competition. Is there a way to see what calls get "paused" for GC?

Depending upon which GC algorithm you are using, it might be no calls, e.g. some GCs run in separate threads, without pausing any of your computation threads.

makes sense. I'll read more on the subject!

what is a non-sequence called in Clojure? In traditional lisps, non-lists are called atoms. But Clojure uses the word atom for something else.

Don't think there's a general name for that. At least never heard of one.

I normally just call things as they are: list, vector, map, set, symbol, keyword, number, string, etc.

I think no one will be offended if you refer to it as a scalar

As far as I can tell, side effects are okay in reduce? Is that correct?

Yes, reduce is strict

thanks!

Take a look at run! for example. It is implemented with reduce

scalar? that's a pretty good name actually

can someone remind me the idiom to use with try/`catch` to catch the exception if a condition, else don't catch it, or perhaps rethrow it? I was looking for an example in the https://clojuredocs.org/clojure.core/try and https://clojuredocs.org/clojure.core/catch, but I didn't see any.

should I simply call throw on the given exception? will that destroy the stack trace?

Yes, calling throw on the given exception should do what you want. And it shouldn't destroy the stack trace. Also before throwing you have full access to the given exception meaning you can build new exception based on the stack trace from the one given

I don't need it now, but if I test the exception object and decide to rethrow it, is it still subject to the other (catch ...) clauses in the same (try ...)? That could be good or that could be bad depending on the situation. It would be excellent if that were specified behavior.

Am I missing a clojure.core fn to get the dispatch val of a multi-method given some input, I thought it would go hand in hand with get-method but I can't see anything obvious. Would it be bad to use ((.dispatchFn ig/init-key) "blah" "blah") or is that unlikely to change?

Does anyone here also program in Scala? If so, maybe you can help me answer a https://clojurians.slack.com/archives/C16LEKSLT/p1604667792002600?

how do you deal with exceptions that happen in anonymous functions that run in a future?

I had to run the code without the future and de-anonymize the function to even get the exception to show up instead of being silently discarded, it was quite the painful debugging experience

yes, it is unclear from documentation but expressions in catch evaluated outside of try context

should I not use futures for non-trivial work?

ah, it was slingshot's throw+ / try+ that somehow hid all that

you can write defmulti with a var in place of dispatch function

(defmulti foo some-dispatch-fn)

(some-dispatch-fn "blah")

Hi all, "lein ring server" command is for starting ring server, what is the command to stop already running server?

It should behave like Java does. So if the exceptions in the catches are in an inheritance hierarchy the most specific one is the one caught. A re-throw would not be caught in the same try-catch but, obviously, any finally expression is eval'ed at the end.

Hi! What is an easy way to save different configurations for test and production? I want to use a different database name when running tests and a different database for development/production code when not running tests. I first thought of hardcoding the database name in the dbfuncs.clj file (using def. But then I changed it to a function. I need to now add code that reads the database name from somewhere. Is it possible to say something like: if running tests then use dbname gamesdbfortest and if not running tests then use dbname gamesdb?

(def hds-opts (atom nil))

(defn db-config
  [dbname]
  {:dbtype "postgres" :dbname dbname})

(defn set-datasrc 
  [dbname] 
  (let [^HikariDataSource hds (connection/->pool HikariDataSource (db-config dbname))]
    (reset! hds-opts (j/with-options hds {:builder-fn rs/as-unqualified-lower-maps})))) 

there's environ and lein-environ, works well for me

Not sure if it’s relevant, but in Java every non-main thread discards unhandled exceptions by default, but you can change that behaviour as described here: https://stuartsierra.com/2015/05/27/clojure-uncaught-exceptions

thanks, I'll add that, even though I mostly use futures

(Hopefully) simple question about clj-time: Is it possible (and if so, how) to get out non-traditional date values? For example, I would like to get day-of-year, week-of-year and day-of-week from a parsed UTC date.

I suppose on day-of-week can just translate from text abbreviation to a numeric value, so nvm about that one. 🙂

@lkottmann Thank you. Will look into environ. I am using deps.edn so the other may not work.

Anyone has deps.edn examples for environ? I see only lein and boot examples in the readme.

Hi guys, can anyone help me and translate the following code snippets into json structure or something I could understand. I don't have a Clojure background and I need to recreate a similar structure in a javascript. i will appreciate your help

(merge {:event/stream :users
                           :event/partition-key user-id
                           :event/type :users/created
                           :event/actors #{:user-id :referring-user-id}
                           :user-id user-id
                           :referring-user-id referring-user-id}
                          (select-keys new-user [:first-name :last-name :username :email]))

{:event/type :users/created
                   :event/created-at (java-time/instant)
                   :user-id #uuid "d415fb11-3d42-4a5d-911e-484b1baad7af"}

Pretty sure futures are dispatched on non-main threads, so unless your code is catching exceptions and doing something with them, they’ll disappear silently (as per JVM default behaviour).

the translation is trivial, what's the specific issue you are having?

{:foo/bar baz} in a clojure data literal becomes {"foo/bar": baz} in json

or "foo_bar" if you prefer - json doesn't have namespaces so there's no direct equivalent

does it mean the

{:event/type :users/created
                   :event/created-at (java-time/instant)
                   :user-id #uuid "d415fb11-3d42-4a5d-911e-484b1baad7af"}

{"event/type": "users/created", 
"event/created": "2020-06-02T21:34:33.616Z",
"user-id": "d415fb11-3d42-4a5d-911e-484b1baad7af"
}

Thank you @noisesmith for a quick reply

(println (json/generate-string {:event/type :users/created
                        :event/created-at (java-time/instant)
                        :user-id #uuid "d415fb11-3d42-4a5d-911e-484b1baad7af"}))

{"event/type":"users/created","event/created-at":"2020-11-06T16:02:42.287334Z","user-id":"d415fb11-3d42-4a5d-911e-484b1baad7af"}

you can check what it serializes to to double check your work. or let cheshire do the work for you

the json alias here is cheshire.core

Great! As I think that's all what I need to know 🙂 Thanks guys and have a good weekend!

@mafcocinco As one of the clj-time maintainers, I'll remind you that the library is deprecated and we recommend folks use Java Time instead, either directly via interop or through one of the available wrappers (which are listed on the clj-time README).

cool thanks.

No, a thrown exception inside the future is returned as the value of the future

And the future :status will be :failed

which libraries do you use for data visualization? (charts / graphics)

Hi, I'm trying to get a Clojure+ClojureScript project working with figwheel-main. I'm somewhat stymied by CORS errors -- do I need to allow calls from localhost:9500 on my server at localhost:8080 or is there any way to just serve everything from the same port?

https://github.com/metasoarous/oz

https://github.com/juxt/aero is a very good library for managing different environments

I think it's just Ctrl-c to kill the process. Using wrap-reload with ring can reduce the need for restarting the server, although it's still required when adding dependencies.

Use doseq if its only side effects

Adding Access-Control-Allow-Origin and Access-Control-Allow-Credentials to the headers works. I guess that'll be that.

The problem comes from futures that I never dereference

Are they ever cleaned up btw?

you can configure your cljs output options and a "wrap-resource" ring middleware to serve the cljs from the same port that you serve your site pages

When the reference to the future is gone, it will be garbage collected

Why would you care about a failed future you don't deref? This fire and forget behavior would imply to me that you choose to not care about what happens to the task

True, I do use scalar for non collections

I can serve the js which figwheel builds but it doesn't live reload for me (although it does fix the cors issue). I've been using ` (defn app [] (html [:head [:title "Welcome to blah"]] [:body [:div {:id "app"} [:script {:src "cljs-out/dev-main.js"}]]]))`

I think Figwheel uses websockets to make live reload work. In that case, you might have to forward websockets traffic as well as static files. I would start by looking for websockets traffic in the browser's network monitor.

forgot to press enter, sorry! Unfortunately in my case I don't own the defmethod, it's integrant/init-key, the method it uses is anonymous and delegates to a private method, .dispatchFn worked fine for me for now, just suprised there wasn't something in core for it

Thanks, I actually was replacing a bit of code that was using a doseq as I needed it sometime to be side effecting and othertimes not and to give back all of the values. reduce gives me the best of both 👍