when should i use sequence instead of seq?

sounds like the answer is if working with transducers or if you want the property of nil returning ()

I don’t think I’ve ever used it in 10 yrs of Clojure

is there any good actor library in clojure?

@i There's Akka / Okku and Quasar / Pulsar, I haven't used the latter so I can't tell you if one is better than the other.

@dacopare actually i doubt the usefulness of a dedicated actor library.

i feel more like, a library will put too much constraints. actor, however, being a model, is a good pattern to follow.

Isn't that the point of these libraries, that they let you follow an actor model? Personally, I prefer to stick to core.async-style communicating sequential processes (CSP).

actors have their own set of constraints and they are not minimal either

especially on the jvm (no per actor gc/heap like on beam)

Maybe you can use akka from clj, I bet it's quite hairy but maybe interop is better nowadays

I sometimes see clojure code online that does this (,,,) at the end of expressions. What is the purpose of this?

I know they are essentially blanks, but why 3, why not just put nothing, or nil?

Used in examples as an ellipsis, a visual cue to indicate more forms may follow here

cf. http://blog.fogus.me/2013/09/04/a-ha-ha-ha-aah/ -- mentioned in the book "clojure applied" and called the "Fogus comma", apparently

I'm actually planning on finishing that book this week. Get a week off work so planning some book time

I found it interesting sisnce I only recently found it that it references schema, but then saw it hasn't had an edition update yet

for some reason cider repl not showing gui from swing i initialize it just returns object.. but normal repl outside works fine ,any1 had this problem?

@mirza are you using SwingUtilities/invokeLater to ensure you're on the swing thread when doing your swing calls ?

it has been years since i've done swing work, but i seem to remember that was a possible problem

@carkh nah havent used invokeLater

@carkh for some reason on other repl not cider it works fine

i think a standard repl is on the main thread while nrepl isn't

could be

thats what i thought

it's good practice to always use invokeLater at the entry point of your swing calls anyways

yea will check

also those pesky swing windows love to hide behind emacs

nah just checked emacs not problem works fine with eshell and lein repl command

@carkh spiral works fine , so problem is somewhere in cider

spiral uses unrepl rather than nrepl, don't know how this one works at all

yea

prep

That works for me in cider

@mirza except that bug in the close function =)

hmm thanks

and it pops up gui ?

seems that my cider is problem then

a small window which is only the title, behind emacs

yea cool,doesnt work for me

will reinstall

i doubt this would help

im'm on windows though, so this might be different

hmm

will analyze it later thanks anyway 😄

good luck

what is a good way to read back in errors printed with the #error tag?

e.g i want to define a function read-error such that:

(let [ex  (ex-info "top" {} (Exception. "root"))]
  (= ex (read-error (pr-str ex))))

ex here is an ExceptionInfo object wrapping an Exception Object, so you are asking for a function that reads a printed exception string and makes an Exception object? what problem are you actually trying to solve?

I have a rest api that show the exception in the response body (printed as #error ...) when an exception is thrown when it handles the request

i'd like to reconstruct the exceptions including causes, data etc, so i can rethrow it in the client, which lets me use cider's tooling to inspect the error

In general, a data conveying exception can contain references to mutable objects that are rife with issues if you attempt to serialize them between machines. Are you OK with such limitations?

yeah any limitations are fine, this is just for a quick and dirty debugging session

e.g. objects representing open files/network-connections, etc.

catch the error and then call Throwable->map on it

the fact that it is being printed is not relevant

but when it is printed, it will be the representation of Throwable->map

Ok, this avoids requiring a reader for 'tag which is nice, but is there a good way to convert this back to a throwable?

you already have an exception when you catch it

yes, but that is only on the server side, i'd like to transfer it to the client so i can rethrow it there

my client and server have the same code base, so if i could do something like

(let [response (call-server)] 
  (when (= 500 (:status response))
    (throw (parse-error (:body response)))))

while it's not impossible, I suspect making that work would be fairly tedious. in particular constructing the StackTraceElements

error data is better than stack traces

i don't know why you'd want to re-read and throw

something will have to re-catch

if you're going between jvms, you could just use Java serialization (but beware of having all the right classes in both jvms)

I've been down that road and it was full of all kinds of exciting pain

@chrisblom while not a Clojure specific solution, I wonder if it would be worth checking out Google Cloud's Debugger https://cloud.google.com/debugger/ - it allows you to inspect running code when an exception happens without performance impact. I haven't used it but sounds like might fit your requirements .

@chrisblom is it possible to just connect CIDER to your server?

don't know if this is a local dev server or 50 kubernetes managed servers though 🙂

oh no, the server is actually running in the same jvm process. I was just curious if it was possible 😁

Sketch of rethrowing exceptions after tranfering them:

(import '[org.apache.commons.codec.binary Base64])

(defn- decode-str [s]
  (Base64/decodeBase64 (.getBytes s)))

(defn- encode-str [bytes]
  (String. (Base64/encodeBase64 bytes)))


(let [caught-exception (->> (Exception. "root" )
                            (Exception. "b")
                            (Exception. "a")
                            (ex-info "top" {}))
      ex-response {:status 500
                   :body (-> (with-open [fos (java.io.ByteArrayOutputStream.)
                                         oos (java.io.ObjectOutputStream. fos)]
                               (.writeObject oos caught-exception)
                               (.toByteArray fos))
                             encode-str)}]
  (throw
   (with-open [fos (java.io.ByteArrayInputStream. (decode-str (:body ex-response)))
               oos (java.io.ObjectInputStream. fos)]
     (.readObject oos))))

👋 Can anyone help me understand the behavior of auto-gensym when used in a function called from a macro? Details in snippet:

the auto gensyming happens at read time

the form is only read once

user=> (read-string "(defn whatever [] `s#)")
(defn whatever [] (quote s__3__auto__))
user=> (eval (read-string "(defn whatever [] `s#)"))
#'user/whatever
user=> (whatever)
s__6__auto__
user=> (whatever)
s__6__auto__
user=>

I think it won't cause a problem in practice, though, for the same reason that using a name in a let binding of a function body won't conflict across function calls.

@hiredman thanks, somehow I've gone on for quite a while without realizing that happened at read time