Clojure Q&A - Recent questions tagged keywords

clojure.edn and clojure allows keywords with empty ("") namespaces

Fri, 05 Dec 2025 09:56:54 +0000

Following links and snippets are about clojure.edn but because this logic is the same in clojure it also affects clojure reader as well.

Here is how symbol pattern is defined:

[:]?([\D&&[^/]].*/)?(/|[\D&&[^/]][^/]*)

It is eagerly matching prefix until the last slash character, after that it matches symbol name.

Then there is a wrong analysis of matched groups happen: ns is incorrectly set to everything until the last slash with validation that it is not ends with :/

Then in Symbol.intern call there is an another lookup for the first slash to split symbol into namespace and name.

The result is that keywords like this: ":/-/-", end up with namespace set to empty string "".

Looks like the least intrusive way to fix it is to use the same logic to find namespace borders in both places:

during symbol reading, lookup the first / to set ns instead of using the first matching group
in symbol interning the logic is correct

Another option is to use different regular expression:

[:]?([\D&&[^/]][^/]*/)?(/|[\D&&[^/]].*[^/])

This matches symbol prefix til the first slash keeping restriction "name can't end with slash".

Keyword internal cache cleaning logic approach

Wed, 21 Jun 2023 11:27:05 +0000

just want to clarify my understanding of that code

	Reference<Keyword> existingRef = table.get(sym);
if(existingRef == null) // keyword was not found
	{
	Util.clearCache(rq, table);  // force cleaning of the dead weak references in the whole cache

           ....create new keyword and store it wrapped into WeakReference in the cache
	}

Maybe i am missing something but what are the reasons/assumptions to force cache clearing from dead weak references on every cache miss if rq is not empty, i.e. there is seq scan of the whole cache to locate dead references and to remove them.
And seq scan is executed during Keyword function calling, i.e. blocks the caller.

Naive alternative is to dedicate a thread which collects the garbage from the cache with a some period (~10 seconds or smth like that)

Could some calls to clojure.core/= be replaced by clojure.core/identical?

Thu, 02 Mar 2023 22:47:18 +0000

I'm using core.cache in combination with LazyMap. Lazy maps are map-like objects (new data type encapsulating maps and adding some logic to auto-force delayed values associated with keys).

When I started putting lazy maps as values of FIFO Cache I observed that all values are being realized just after the map lands in cache. After some digging I've found that it is caused by expression (= ::expired v) in clojure.core.cache.wrapped/lookup-or-miss.

What happens is that = internally calls clojure.lang.Util/equiv (since LazyMap implements IPersistentCollection) and then, after some dispatching, equiv is called to check whether the contents of a lazy map equals to other object (implicitly other map). This is the desired behavior and lazy map realizes all values to make comparison possible.

However, when comparing a map-like object to something which is not a map (nor a collection), short-circuit would be welcome as soon as we know that it will for sure return false. But changing that is probably more related to Clojure itself and things like CLJ-1375.

What could be done on core.cache's side, if that's not too problematic, would be a replacement of

(= ::expired v) with (identical? ::expired v)

in clojure.core.cache.wrapped.

It would not only fix corner cases like mine but also speed things up a bit (explicit referential equality rocks when it comes to Clojure keywords).

Other expressions where that could be changed (just in case) are:
(= ::nope ret) and (= ::nil v) from clojure.core.cache.

The `keyword` and `symbol` docstrings don't mention that using `"a/b"` as its only argument is valid

Wed, 08 Feb 2023 16:53:38 +0000

The current docstrings:

clojure.core/keyword
([name] [ns name])
  Returns a Keyword with the given namespace and name.  Do not use :
  in the keyword strings, it will be added automatically.

clojure.core/symbol
([name] [ns name])
  Returns a Symbol with the given namespace and name. Arity-1 works
  on strings, keywords, and vars.

The arglists suggest that the first arity is to be used for simple idents only.
However, the underlying implementation explicitly handles the case when there's / in the value, and even the argument is named nsname:

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));
}

One example where some existing code relies on this behavior: transit-clj

Perhaps, the docstrings should be updated to reflect that?

Shouldn't Keyword extend AFn like Symbol?

Sun, 11 Dec 2022 08:59:35 +0000

In source code I have noticed that Keyword class doesn't extend AFn and there are a lot of invoke declarations, which can be removed by extending AFn. And for that purpose AFn, I suppose, exists.

So why Keyword doesn't extend AFn? And comparing with Symbol behaviour, shouldn't it be considering as a bug?
`
(instance? clojure.lang.AFn :asdf)
=> false

(instance? clojure.lang.AFn 'asdf)
=> true
`

Add function that returns every interned keyword in the runtime

Wed, 07 Sep 2022 18:18:21 +0000

Having access to a list of every interned keyword in the runtime is useful for implementing editor auto-completion and other editor integration features.

Currently, most tooling does something like this:

user=> (let [field (.getDeclaredField clojure.lang.Keyword "table")] (.setAccessible field true) (map keyword (.keySet (.get field nil))))
(:target :clojure.main/message :clojure.spec.alpha/unknown :datafy :clojure.core.specs.alpha/prefix :dir :clojure.core.specs.alpha/binding-form :allow ...)

However, this approach relies on reflection to grab hold of a private, static field. The underlying bits are presumably (albeit unlikely) subject to change without notice.

Would it be possible to add a function into clojure.core that returns a list of all keywords in the runtime? Perhaps (all-keywords) (like (all-ns)). Or perhaps a public static method to clojure.lang.Keyword?

See also grep.app results for this pattern.

Error when deserializing a keyword after upgrading from Clojure 1.10.3 to 1.11.0 (java.io.InvalidClassException)

Tue, 29 Mar 2022 15:04:10 +0000

I have recently updated our application from Clojure 1.10.3 to 1.11.0 and we are now facing deserilization issues when reading an object serialized by the former version via Quartz (scheduler).

This is the error we are getting:

....
org.quartz.impl.StdScheduler.getJobDetail StdScheduler.java: 498
org.quartz.core.QuartzScheduler.getJobDetail QuartzScheduler.java: 1518
org.quartz.impl.jdbcjobstore.JobStoreSupport.retrieveJob JobStoreSupport.java: 1374
org.quartz.impl.jdbcjobstore.JobStoreSupport.executeWithoutLock JobStoreSupport.java: 3739
org.quartz.impl.jdbcjobstore.JobStoreTX.executeInLock JobStoreTX.java: 93
org.quartz.impl.jdbcjobstore.JobStoreSupport.executeInNonManagedTXLock JobStoreSupport.java: 3803
org.quartz.impl.jdbcjobstore.JobStoreSupport$9.execute JobStoreSupport.java: 1377
org.quartz.impl.jdbcjobstore.JobStoreSupport.retrieveJob JobStoreSupport.java: 1385
org.quartz.impl.jdbcjobstore.StdJDBCDelegate.selectJobDetail StdJDBCDelegate.java: 860
org.quartz.impl.jdbcjobstore.StdJDBCDelegate.getObjectFromBlob StdJDBCDelegate.java: 3201
java.io.ObjectInputStream.readObject ObjectInputStream.java: 460
...
java.io.ObjectStreamClass.initNonProxy ObjectStreamClass.java: 699
java.io.InvalidClassException: clojure.lang.Keyword; local class incompatible: stream classdesc serialVersionUID = -2105088845257724163, local class serialVersionUID = 2404715664513862299
org.quartz.JobPersistenceException: Couldn't retrieve job because the BLOB couldn't be deserialized: clojure.lang.Keyword; local class incompatible: stream classdesc serialVersionUID = -2105088845257724163, local class serialVersionUID = 2404715664513862299

I'm wondering if the problem is that Keyword.java has changed recently
and because it doesn't declare it's own serialVersionUID it got a new one.
Is there any reason why the Keyword class doesn't declare its own serialVersionUID? Can we get it fixed?

clj-uuid/v5 uuids inconsistent after Clojure 1.11.0

Wed, 23 Mar 2022 14:21:43 +0000

Hi, i’ve come across the following when updating to Clojure 1.11.0. In our application we have some places where we create V5 (name based, SHA1 hash) uuids, using the danlentz/clj-uuid library. After the upgrade the v5 uuid’s produced are different. An example being:

(def ^:const +namespace+ #uuid "50d94d91-a1cf-422d-9586-4ddacf6df176")

(clj-uuid/v5 +namespace+ :some-keyword) 

;; Clojure 1.10.3
=> #uuid "d30e9c3c-ced2-534e-a6b8-ecf784fb0785"

;; Clojure 1.11.0
=> #uuid "a16f6719-952a-55b9-b71b-b15dd263665b"

After some trial an error It seems it is the local part argument i.e :some-keyword that is causing the difference, as within the clj-uuid/v5 fn it converts the keyword Object to a ByteArray, which now appears to be different. (If I use a String instead of a keyword for the local part argument then the uuid produced is consistent before and after the Clojure upgrade.)
The uuids produced are used in downstream systems and It would be quite difficult to have them handle the change. Is there anyway that I could achieve the exact same previous uuids?

When to use simple/qualified keywords?

Fri, 26 Mar 2021 13:47:38 +0000

Is there any "official" guidance on this?

Clojure.spec uses both:

(s/def ::foo (s/keys :req [::bar]))

The current usecase I'm wondering about is an internal API I'm working on. It is pretty clear that top-level keys in the api response benefit from being qualified. How about keywords in value positions?

{:my.api.person/name "Imre"
 :my.api/result-type :success ;; :my.api.result/success perhaps?
 :my.api/warnings [:quota-exceeded :my.api.quota/exceeded]}

Edit: Slack discussion where I brought this up first

defrecord qualified field names

Sat, 06 Feb 2021 21:17:36 +0000

Coming from a RDF background I tend to use qualified keywords a lot when defining properties. However after looking at the Reitit HTTP router it appears that defrecord is really benefitial for performance. This often leads me to a choice between performance or clean data representation when designing software.

In order to avoid this dilemma, I think it would be nice if defrecord could support something similar to what is already done for map destructuring

(def m {:domain/id 14 :other/id "UV"})

(let [{:keys [domain/id]} m] id)
;;; ⤷ 14

We could have something like

(defrecord Employee [domain/id domain/full-name]
  Object
  (toString [_]
    (str "<< id: " id ", name: " full-name " >>")))

(def alyssa (->Employee 14 "Alyssa P. Hacker"))

(.toString alyssa)
;;; ⤷ "<< id: 14, name: Alyssa P. Hacker >>"

(:domain/id alyssa)
;;; ⤷ 14

where:

the name part is bound in the record definition and is used as the Java internal class field
the fully qualified identifier is used when accessing/manipulating the record objects from its map-like interface.
collision in the field names would throw

I have implemented a prototype to demonstrate how it could be done in practice. I wonder if such extension has already been considered for clojure.core/defrecord and if there are some design/implementation issues that I am overlooking.

Listing all keywords in a namespace

Wed, 13 Jan 2021 17:04:23 +0000

In clojure, symbols can optionally belong to a namespace:

:FileType/TXT

Is it possible to list all keywords that are defined for a given keyword namespace?

is there a version of pr-str that emit full versions of qualified keywords in maps instead of short forms?

Fri, 10 Apr 2020 07:54:25 +0000

Something like {:foo/bar 1} instead of #:foo{:bar 1}
I need to debug some edn and it's impossible to jump to the desired keywords if they're in the short forms.

What is keywords for clj used for? What do they actually mean and do?

Fri, 27 Mar 2020 09:04:53 +0000

I learned about keywords a while back, but Im not sure what they are actually used for outside of for keys in maps. Are there other uses for keywords outside of maps?

Also what do they actually mean and do?

How to read namespaced keywords with clojure.tools.reader/read?

Mon, 18 Nov 2019 14:04:04 +0000

I'm using clojure.tools.reader/read for reading clojure and cljs forms from files.

Everything works fine but reading namespaced keywords like ::keyword get read as :user/keyword.

I know the reader uses ns dynamic var to figure out the current namespace for reading symbols and keywords but I don't know how to use it to read a non existing namespace, like the one from the file I'm just reading.

I'm trying a (in-ns file-ns-symbol) before doing the read so it creates the ns before reading and it works but sometimes I'm getting java.lang.IllegalStateException: Can't change/establish root binding of: *ns* with set

Just doing

(binding [*ns* file-ns-symbol]
  (reader/read ...))

doesn't work since it will try to call (the-ns file-ns-symbol) for a ns that doesn't exist.

Any ideas or pointers on how to do this?

Thanks!

Transducers and Maps

Tue, 24 Sep 2019 20:14:24 +0000

Hi,

I'm learning more about transducers, but coming up with some deadends.

What I'm looking to understand, is whether they are appropriate to use (in my use-case, but also as a learning exercise) and whether what I am doing is right/efficient/maybe-there-is-a-better-way :-)

Let' say I have a data stucture thus:

 (def trip {:tripData 
            {:segments [{:dataPoints 
                         [{:location {:lat 1 :lng 2}} 
                          {:location {:lat 3 :lng 4}}]}]}})

There could be hundreds/thousands of dataPoints with each dataPoint having a single location.

I want to efficiently extract out only the lat and lng into a single collection and turn it into a string. I came up with this:

 (def xf
   (comp
    (mapcat :dataPoints)
    (map :location)
    (map (fn [{lat :lat lng :lng}] (str lat " " lng)))))

then evaluated via:

(def lat-lng (into [] xf (->> trip :tripData :segments)))

And I get back something like this:

["1 2" "3 4"]

Which I can then do (for the purposes of my exercise), this:

 (clojure.string/join ", " lat-lng)

to obtain, finally, this:

"1 2, 3 4"

Which is all fine and dandy :-)

However, given my inexperience with transducers, I'm left wondering if there is a different/better way. For example, a way, within the comp xf, to turn the data into the string and joined at the end instead of using clojure.string/join.

I also discovered, I can do this too, without the use of transducers:

 (def lat-lng-2 (->> trip
                     :tripData
                     :segments
                     (mapcat :dataPoints)
                     (map :location)
                     (map (fn [{lat :lat lng :lng}] (str lat " " lng)))))

Which, given the clojure.string/join, ends up with the same result.

However, it's my understanding that you can't use a map keyword (i.e., :tripData, :segments) as part of a comp as keywords are not transducers.

I'm at a loss on how to make this efficent/better whilst learning how I can use transducers.

I would appreciate some help/guidance/feedback!

Thank you.