It seems Clojure install guide doesn't reall walk you through to how to install Java

And it appears however you install Java, the clj cli expects you to set JAVA_HOME

Does that seem correct? If someone has Clojure installed and working, thus I can safely assume that JAVA_HOME is set as well ?

You are asking if it is possible to set up an environment that runs Clojure without setting the JAVA_HOME env variable? I would guess it is possible, at least. I do not know whether it is common to do so.

I don't really install java, just download the jdk and set my bashrc to add the path to the bins

Hum, not exactly. I'm asking if setting up Clojure requires you to setup the JAVA_HOME environment variable.

clojure uses java, and java has to be on the path. I think java_home is a fallback used by many programs if java isn't available?

through installation I mean

I am attempting to try out a fresh install of Clojure on an Ubuntu Linux system to confirm, but I am pretty sure I can follow the Clojure getting started steps, installing a JDK in a way that does not assign a value to the JAVA_HOME env variable, and the clj and clojure commands will still work. Will report back what I find.

interesting

This is the code for the clojure command to find java:

# Find java executable
set +e
JAVA_CMD=$(type -p java)
set -e
if [[ ! -n "$JAVA_CMD" ]]; then
  if [[ -n "$JAVA_HOME" ]] && [[ -x "$JAVA_HOME/bin/java" ]]; then
    JAVA_CMD="$JAVA_HOME/bin/java"
  else
    >&2 echo "Couldn't find 'java'. Please set JAVA_HOME."
    exit 1
  fi
fi

So it seems it first tries $(type -p java) which I do not know what that does. And if that didn't work, it tries to look for JAVA_HOME, I think that's correct, my bash isn't great

yeah, if you didn't install java via some installer, where it sets the path so it appears callable, then it falls back to the java_home. I ran into this long ago with intellij tools

Ok, type is a linux command, I'm guessing available on mac as well

On an Ubuntu 18.04 system where I had never installed Clojure before, but did have OpenJDK 11 installed via an Ubuntu/Debian package, and there was no JAVA_HOME variable assigned a value in the environment, I can follow the Linux install instructions on Clojure's get started page, and both clojure and clj commands run without complaint.

The output of type -p java on that system is /usr/bin/java , which is where the java executable is installed by the Ubuntu/Debian package

The bash command page describes what the type built-in command does.

buried within that many-pages-long man page 🙂

Ok cool. I could probably use that logic too. Though it seems there is also a way using java itself: java -XshowSettings:properties -version which prints a bunch of info, one of them being where java is installed

Seems more reliable, I might go with that

If you are assuming bash exists, then type command exists, too.

I think that will work on windows as well

Wndows without WSL tends to be enough different from macOS/Linux that it often needs it own way of doing things.

ya, I don't know how much I should bother for windows. Do people even use Emacs on windows 😛

I have before, but not recently. It exists.

If you do not polish/test/support Windows, you will not be alone 🙂

😛

Is there a simple way to have clj install the deps and do nothing else?

How can I debug "Error building classpath. Could not find artifact ... in central"? I'd like to know what the resolved dependency is that doesn't have its own dependency in central.

Anyone knows what is this error when using aws-cli?

(def s3 (aws/client {:api :s3}))
(aws/validate-requests s3 true)

(aws/invoke s3 {:op :ListBuckets})

=>
{:cognitect.anomalies/category :cognitect.anomalies/fault,
 :cognitect.anomalies/message nil,
 :cognitect.http-client/throwable
 #error
 {
  :cause nil
  :via
  [{:type java.nio.channels.ClosedChannelException
    :message nil
    :at [.FillInterest onClose "FillInterest.java" 150]}]
  :trace
  [[.FillInterest onClose "FillInterest.java" 150]
   [.AbstractEndPoint onClose "AbstractEndPoint.java" 354]
   [.ChannelEndPoint onClose "ChannelEndPoint.java" 216]
   [.AbstractEndPoint doOnClose "AbstractEndPoint.java" 225]
   [.AbstractEndPoint close "AbstractEndPoint.java" 192]
   [.AbstractEndPoint close "AbstractEndPoint.java" 175]
   [.ssl.SslConnection$DecryptedEndPoint doClose "SslConnection.java" 1132]
   [.AbstractEndPoint doOnClose "AbstractEndPoint.java" 220]
   [.AbstractEndPoint close "AbstractEndPoint.java" 192]
   [.ssl.SslConnection$DecryptedEndPoint onFillable "SslConnection.java" 425]
   [.ssl.SslConnection onFillable "SslConnection.java" 305]
   [.ssl.SslConnection$2 succeeded "SslConnection.java" 159]
   [.FillInterest fillable "FillInterest.java" 103]
   [.ChannelEndPoint$2 run "ChannelEndPoint.java" 118]
   [org.eclipse.jetty.util.thread.strategy.EatWhatYouKill runTask "EatWhatYouKill.java" 336]
   [org.eclipse.jetty.util.thread.strategy.EatWhatYouKill doProduce "EatWhatYouKill.java" 313]
   [org.eclipse.jetty.util.thread.strategy.EatWhatYouKill tryProduce "EatWhatYouKill.java" 171]
   [org.eclipse.jetty.util.thread.strategy.EatWhatYouKill run "EatWhatYouKill.java" 129]
   [org.eclipse.jetty.util.thread.ReservedThreadExecutor$ReservedThread run "ReservedThreadExecutor.java" 388]
   [org.eclipse.jetty.util.thread.QueuedThreadPool runJob "QueuedThreadPool.java" 806]
   [org.eclipse.jetty.util.thread.QueuedThreadPool$Runner run "QueuedThreadPool.java" 938]
   [java.lang.Thread run "Thread.java" 834]]}}

I think it might be some kind of SSL issue? But I have no idea how to solve it. I can list the buckets using aws-cli on the command line without issue

if I have a fully qualified symbol, how do I get a non-qualified symbol? I want to strip the namespace off.

but I want the output as a symbol

i guess not this?

(def a 'clojure.string/split)
(symbol (name a))

that works 🙂

I think that's the most straightforward way too lol as Symbol has

final String ns;
final String name; 

public String getName(){
	return name;
}

static public Symbol intern(String nsname){
	int i = nsname.indexOf('/');
	if(i == -1 || nsname.equals("/"))
		return new Symbol(null, nsname);
	else
		return new Symbol(nsname.substring(0, i), nsname.substring(i + 1));
}

fwiw, i also looked at the Symbol.java file to see if there might not be some interop / obvious better way 🙂

😁

It’s not a single fn call for a reason, I think.

You’re taking something that’s very specific and has well-defined semantics and turning it into something unspecific with loose semantics.

It’s a good recipe for wasting time.

Hi, is it possible to have a catch all declaration in a compojure route? Something like: (POST "/api/invoke/:rest-of-thing/" [rest-of-thing req] (invoke-post rest-of-thing req)) where rest-of-thingcan be any uri like foo/bar/baz or /buz/3/5/id?

I’m testing a function that uses a core.async channel. For the tests, I wrote a simple timeout-chan function. Here is a simple version of its implementation:

(let [in-chan  (a/chan)]
    (a/go (a/<! (a/timeout 1000))
          (a/close! in-chan)
  (apply function-using-async in-chan))

I have seen this pattern used in the wild:

(let [v _] (async/alts!! [chan (async/timeout 1000)]))
  (assert (nil? v))
  (is (= 5 (count v)))
  ; ...other assertions

Are classes not valid keys in a case?

(case Integer Keyword "keyword" Integer "integer") 
=> Execution error (IllegalArgumentException) at spectrum.repl/eval27661 (form-init14549903441455335896.clj:514).
No matching clause: class java.lang.Integer

@arohner I believe those “classes” are resolved as symbols.

(case 'Integer
  Integer :int
  String :str)

=> :int

In Clojure, you can’t refer to classes as primitives – they’re referred to through symbols.

So, to answer your question: I don’t think use case to dispatch as you would want.

Thanks. I’ve made it work with symbols of classnames

Whats the equivalent of a "rest" let destructure for map destructuring? For example, for list its simple: (let [[x & rest] [:a :b :c]] (println rest)) This prints (:b :c) as expected

However, I can't seem to find how to do it for map destructuring

so that: (let [{x :a & rest} {:a :a :b :b :c :c}] (println rest)) returns {:b :b :c :c}

Doesn't seem to work 😞

What do you want back?

I want the object thats left after remove :a from the original map (ie the rest)

That’s not how it works

so {:a :a :b :b :c :c} (pick :a out and return rest operation) => {:b :b :c :c}

That’s not a thing

You can dissoc :a from the full map in a second binding

ah gotcha, thats what I need thanks!

Hi! I have a weird compile error: > Syntax error (IllegalArgumentException) compiling . at (src/../run.clj:7:28). > Unable to resolve classname: clojure.core$double@4d1947e7 in this code

(Math/round (months-between-approx from to))

(defn ^double months-between-approx [^Instant i1 ^Instant i2] (/ .. 30.5))

Move ^double after the function name (so it's in front of the arglist).

Putting metadata ahead of the function name causes it to be evaluated (to the clojure.core/double function) and then added as a :tag I think. Putting it before the arglists will do what you want.

^ @holyjak

user=> (defn ^double foo [] 1.0)
#'user/foo
user=> (+ 1 (foo))
Syntax error (IllegalArgumentException) compiling . at (REPL:1:1).
Unable to resolve classname: clojure.core$double@5da7cee2
user=> (defn foo ^double [] 1.0)
#'user/foo
user=> (+ 1 (foo))
2.0
user=>

Thanks a lot! Frankly, I never remember where to put the return value tag. My reasoning was that if it was before the arglist, it would be metadata on the arglist, not on the function. I should have just checked the docs 😅

And metadata on the arglist is exactly where you want it 🙂

user=> (defn ^double foo [] 1.0)
#'user/foo
user=> (-> #'foo meta)
{:tag #object[clojure.core$double 0x187e2f02 "clojure.core$double@187e2f02"], :arglists ([]), :line 1, :column 1, :file "NO_SOURCE_PATH", :name foo, :ns #object[clojure.lang.Namespace 0x5b5babb "user"]}
user=> (defn foo ^double [] 1.0)
#'user/foo
user=> (-> #'foo meta)
{:arglists ([]), :line 3, :column 1, :file "NO_SOURCE_PATH", :name foo, :ns #object[clojure.lang.Namespace 0x5b5babb "user"]}
user=> (-> #'foo meta :arglists first meta)
{:tag double}
user=> 

For a lot of things, it will work before the function name -- when the metadata is the same evaluated as unevaluated. And of course there are situations where you want the metadata on the function instead of the arglist.

Just found this: clojure bot for eval clojure code on slack. Maybe we can have this on our group? https://github.com/verma/clj-slackbot