Silly question, but following along in the https://clojurescript.org/news/2018-03-26-clojurescript-command-line#starting-a-browser-repl I am entering the following

> java -cp cljs.jar cljs.main
Exception in thread "main" java.net.BindException: Address already in use (Bind failed)

How do I diagnose/modify what port is being used and causing an error?

Getting pretty much the same thing from https://clojurescript.org/guides/quick-start#clojurescript-compiler as well:

inferno git:(master) ✗ clj --main cljs.main --compile inferno.hello --repl
Exception in thread "main" java.net.BindException: Address already in use (Bind failed)

@samedhi By default it is port 9000

@mfikes lsof -n -i4TCP | grep 9000 gives me nothing, am I doing something dumb?

I'm not sure if the default is easily controllable https://clojurescript.org/reference/repl-options#_browser_repl_options

Try telnet 0 9000 as another test to be sure nothing is listening on TCP there

WTH?

hello-world telnet 0 9000
Trying 0.0.0.0...
Connected to .
Escape character is '^]'.

… what have I done?

Hah! Nice. WTF.

You may have some port forwarding set up? Stange.

Got it @mfikes, think you are right, I’ll figure this out, at least I know it is me and not something actually wrong with the process.

Unless you have something odd in your /etc/hosts file. Hrm.

Right, problem is on your end unfortunately. It is unfortunate that you can't easily change the browser REPL port to something other than 9000 😞

You helped me along, I’ll twiddle with it some more, thank you for your help!

FWIW, the port is controllable. I just don't know how to do it via the configuration you can pass via cljs.main. You could clone and build the compiler with a different port, but that might be too much.

Ugh, ok, the key for me was the fact that everytime I kill the PID, a new process spun up at the same port.

That was dumb, but all I really needed to do was stop datomic from starting at startup. 🙂

atoms: do you ever constrain the functions that can be applied to an atom, using a certain code pattern? I know this question sounds a little OO, but code robustness is a concern also for functional programs. I was thinking of a generator function that returns the atom alongside the functions that can be operated on it. This just helps with code organization, does not enforce any restrictions. I find it a necessary balance though.

Admittedly, that is actually not very different from just placing all functions interacting with the atom ― in a namespace dedicated to the atom...

@matan An alternative is to add a :validator to an atom that ensures data in the atom always satisfies some invariant.

validators are underappreciated

:thumbsup:

Well, they have a cost at runtime

Anyway, thanks

Could you please remind me what are my options for mapping a collection without holding to its head and realizing it in full in memory? as I understand every element of the source collection is realized and kept in memory even if the only necessary access to it is during the map operation itself.

map doesn't hold onto the head. Not unless you've wrapped it in a doall to force execution for side effects

And even then, if all you care about is the side effects, use dorun

Or (run! fn coll), which neatly combines (dorun (map fn coll) into a single call

@carr0t close, but dorun and doall are synonyms, and run! is implemented with reduce

never mind i'm wrong

dorun and doall are not synonyms

Indeed. doall retains the head. dorun does not

FWIW, the above is true in Clojure, but not in ClojureScript, which doesn’t have locals clearing.

hi all, what would be the fastest way to go from 0 to at least mid level in clojure, this in order to land a job using the tool?

in terms of learning path

many people (including me) began with Clojure for the Brave and True

got it

so do you think that using that I will get at least a grabs with the language ? @joelsanchez?

I have the living clojure book

and was thinking on starting there + the clojure koans

that's probably fine too, I was just citing a very popular and loved book

gotcha

thanks

has anybody had any luck with managing async control flow without using core.async? i started down the cljs-ajax route, but it sure is painful to be back to callback hell

If I'm printing out some data, or writing it to a file, how would I check if a value is a string and if it is, then print it out with single quotes. For example I'm printing the string ASSET How would I add the single quotes so it prints like this 'ASSET'

@jisaacs46: one way to do this would be to make a multimethod on the type of the object, where the method for string returns (str \' s \')

I'm trying to write a string to a file with single quotes like this (->> map-values (map #(str \' % \'))), but all the file has is clojure.lang.LazySeq@19f48b3b how do I get it to actually print out the strings?

map produces a lazy sequence and println doesn't realize the sequence. You could either use mapv to get a non-lazy vector or thread the result into doall @jisaacs46

println does realize a sequence

but I’m assuming he’s not using println

how are you writing the string into the file? spit?

Ah, sorry, that was sloppy of me.

I'm using

(defn write-file [str]
  (with-open [w (  "whfs.sql" :append true)]
    (.write w str)))

what string do you actually want written?

like just pr-str on the original map-values may be closer to what you want

It may be, I'll try it. I'm trying to write a bunch of inserts statements, from a vector of maps i retrieved from the database, to a file

I am currently doing something similar lazily parsing xml log files using data.xml. Since doall retains the head, does it mean that all the data is stored in memory anyway at some point?

@alwyn yes - but you can use dorun instead of doall to not retain the head or return a collection if that works

If I have the following code:

(with-open [rdr (io/reader "/home/alwyn/p/olslogF.txt")]
  (doall
   (->> rdr
        xml/parse
        :content
        (filter is-debug-realm?)
        first)))

first already limits it

debug code 🙂 I'm trying to figure out how to actualize that filter function Currently it doesn't work because all it does is trying to fetch specific keys from the 'current' item in the sequence, but I suspect 'current' is not actualized yet.

the item first sees is realized

so if there is no result, then there must be something wrong with my filter function...