Clojure Q&A - Recent questions tagged namespace

Can: "Alias already exists in namespace" be fixed?

Mon, 26 Sep 2022 13:51:27 +0000

When defining a namespace alias in an ns form, and then later changing the namespace that alias refers to, you get an error:

(ns foo.bar
  (:require [my.xxx :as xxx]))

I evaluate this in my REPL. Later I change it to:

(ns foo.bar
  (:require [other.xxx :as xxx]))

And I get this exception

java.lang.IllegalStateException
Alias xxx already exists in namespace foo.bar, aliasing my.xxx

That's a pretty gnarly sharp edge. Many people won't find a better solution than restarting their REPLs. Experienced Clojure developers will tell you to do

(ns-unalias *ns* 'xxx)

and re-evaluate the ns form, but that's a pretty silly workaround. The right thing to do would be to drop the old alias and pick up the new one.

You'd (I supposed) still have to re-evaluate the code that uses the alias before it gets picked up, but that's fairly consistent with Clojure's mental model IMO.

We can redefine vars, why can't we redefine namespace aliases?

How can I have a clj REPL namespace be the same as the namespace defined in my file.clj?

Fri, 07 Jan 2022 18:47:07 +0000

I am using Emacs/Cider to launch a clj REPL. I do this by first opening my file which defines a new namespace. I then use cider-jack-in-clj to launch the REPL. The REPL namespace is “user”. I can only use fully qualified functions within the REPL. If I enter user=> (ns myns) in the REPL, this works and changes the namespace as expected. I would like to automate this so that every time I launch a REPL from a file the REPL namespace changes as well.

Alternatively, I am ok not changing the namespace as long as I can use unqualified functions.

Here is an example from the top of my file, core.clj

(ns coresync.core
(:use [tupelo.core])
(:require [clojure.core.async :refer [chan >!! <!!]]))

Within the emacs buffer for the code, I am able to get all the unqualified functions, but within the REPL, I need to use:

user=> clojure.core.async/chan

I’ve searched online and through this forum, but I haven’t been able to figure this out. I’m sorry in advance if this has already been asked and I missed it.

Thanks

json writer and namespaces

Thu, 05 Nov 2020 11:50:53 +0000

Hello

I'm new to Clojure and didn't find answer so please sorry if this is not issue at all.

lets say we have data:

{:space1/value 123 :space2/value 456}

and use clojure.data.json as serialiser:

(clojure.data.json/write-str {:space1/value 123 :space2/value 456})
=> "{\"value\":123,\"value\":456}"

As you see result is not what one can expect.
Obvious solution would be to provide own key-fn and forget about it. But I spend a lot of time catching bug caused by default implementation and like to save time of other