Clojure Q&A - Recent questions tagged error

"Nested" vs "lateral" exception causes

Sun, 05 Apr 2026 14:18:26 +0000

Currently, clojure.core/ex-info must take a msg and data map, and may take a cause, which must be another Throwable, which may have its own cause, etc. etc..

This supports the case of "nested" exceptions quite well, e.g. in the case of compilation exceptions being caused by macroexpansion exceptions, potentially with their own cause, and works well for fail-on-first-problem situations.

There's also the situation of "lateral" exceptions, e.g. in the case of test runners or static analysers, which is not supported. In this case, if we take lazytest as a concrete example, the test runner throws an exception if any of the test cases it runs throws an exception, but the overall cause of the overall exception, conceptually, is all the individual exceptions.

Currently, the only to do this is to make some bespoke thing in the data map.

I propose changing clojure.core/ex-info to take [msg map & causes], which would be a non-breaking change (or, while we're at it, make the map arg optional as well and default it to {}, but that's a separate topic).

That leaves the question of how to handle ex-cause. To my understanding, to change it to return the cause or the list of causes, would maybe be a breaking change for general exception handling libraries or something, but would not imo pose any significant problem. Alternatively, we might have ex-causes to always return a list, and change ex-cause to (comp first ex-causes).

Any thoughts? I don't trust myself to spearhead a PR alone on this but I'd love to contribute, certainly the pure-clojure side of things seems straightforward enough (and I'd love to patch this into lazytest, but that's again a different topic).

Typo in the release notes for 1.12.0-alpha6

Fri, 09 Feb 2024 00:51:06 +0000

This under Array Class Symbols

Clojure supporst class symbols

should be

Clojure supports class symbols

#object[db$getnameonly 0x66908383 db$getnameonly@66908383] 1

Fri, 09 Dec 2022 06:35:16 +0000

Hi!
I've been working on a script and I don't understand what this error means.

My function, takes a number (id) and extract the first element of a list in my vector.

Details :

My function :

 (defn getnameonly [number] 
  (doall (nth (
        (nth 
         (filter #(= number (first %)) customers) 
         0) 
        1) 
       0))
  )

where customers is :
(
[1 (John Smith 123 Here Street 456-4567)]
[2 (Sue Jones 43 Rose Court Street 345-7867)]
[3 (Fan Yuhong 165 Happy Lane 345-4533)]
)

So basically, I want to pull out (return value) "John Smith" if I give 1 to my function.

The code :

(nth (
            (nth 
             (filter #(= number (first %)) customers) 
             0) 
            1) 
           0))

works fine outside the function. However, when I call :

(println getnameonly 1)

I get :

#object[db$getnameonly 0x66908383 db$getnameonly@66908383] 1

Any idea why and how to solve this issue?

improve syntax errors on tagged-literals

Wed, 28 Sep 2022 13:24:40 +0000

When we write a symbol in the UUID literal, the reported error message is wrong

(as of 1.11.1)

clojure -M -e '#uuid id'
Execution error (AssertionError) at clojure.main/main (main.java:40).
Assert failed: (string? form)

It is wrong because

It is not an execution error. Should be read or syntax error.
It does not include any ex-data: https://clojure.org/reference/repl_and_main#_error_printing

It should be something like this

Reader error (AssertionError) at clojure.uuid/default-uuid-reader (uuid.clj:12).
Assert failed: (string? form)

A second step improvement could be add spec support to data-literals, as macros do.

Syntax error reading #uuid id at (REPL:1)
id - failed: string? at: [:form]

From #clojure-dev slack channel

Alex: You don’t need anything special there - just an instrumented spec on the data reader fn

After run

(s/fdef clojure.uuid/default-uuid-reader :args (s/cat :form string?))
(clojure.spec.test.alpha/instrument `clojure.uuid/default-uuid-reader)

The message turns into

Syntax error reading source at (REPL:2:1).
Call to #'clojure.uuid/default-uuid-reader did not conform to spec.

This is a way better message.

Also, it includes a #:clojure.error{:phase :read-source} in ex-data.
So the fix could be just add a spec to clojure.uuid/default-uuid-reader

Why i get "No suitable driver found for jdbc:://127.0.0.1/" ?

Mon, 26 Sep 2022 21:45:00 +0000

Java version :

openjdk 18.0.2-ea 2022-07-19
OpenJDK Runtime Environment (build 18.0.2-ea+9-Ubuntu-222.04)
OpenJDK 64-Bit Server VM (build 18.0.2-ea+9-Ubuntu-222.04, mixed mode, sharing)

but when i start the nREPL in my text editor, it's says :

Starting nREPL server...
/usr/lib/jvm/java-11-openjdk-amd64/bin/java ...

Dependencies :

:dependencies [[org.clojure/clojure "1.11.1"]
               [com.github.seancorfield/next.jdbc "1.3.834"]
               [org.postgresql/postgresql "42.5.0"]
               [com.layerware/hugsql "0.5.3"]]

code :

(def db
    {:classname "org.postgresql.Driver"
     :subprotocol "postgresql"
     :subname "reporting"
     :user "admin"
     :password "admin"})

(defn add-user-transaction [users]
  (jdbc/with-transaction [t-conn db]
                         (if-not (find-user t-conn {:id (:id users)})
                           (add-user! t-conn users))))

Everything works normal with that configuration, but only when i evaluate

(add-user-transaction {:id "cheryl"
                   :pass "Cheryl"})

the error appears.

It's asked in Clojure: Execution error (SQLException) at java.sql.DriverManager/getConnection (DriverManager.java:702) and already have answered, but the only answer in there is using :deps or deps.edn (as far i know, this is Maven repository), so how about leiningen? Or did i miss something about leiningen and Maven?
And i even restarting my pc, text editor, and nREPL but nothing change.