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Editorial Team
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Asked: 2026-05-28T03:41:37+00:00

I’m learning Clojure and am messing around on the REPL. For assert , the

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I’m learning Clojure and am messing around on the REPL. For assert, the documentation says 

Usage: (assert x)
   (assert x message)

Evaluates expr and throws an exception if it does not evaluate to
logical true.

So I expected (assert false "Error message") to raise an error and output "Error message". However, it gives 

java.lang.IllegalArgumentException: Wrong number of args (4) passed to: core$assert (NO_SOURCE_FILE:0)

Why does it say I have four arguments, and what would be the correct usage? The documentation to assert is not too verbose.

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1 Answer

  1. Editorial Team

    I just tried it out on 1.2.1 and I get the same behavior as you.

    Then I tried (doc assert) on 1.2.1 in REPL as well:

    clojure.core/assert
([x])
Macro
  Evaluates expr and throws an exception if it does not evaluate to
 logical true.

    It seems that the message was added in 1.3 so you can only use the version with one parameter in 1.2.

    If you are browsing online documentation be sure you are reading the correct version. Whenever in doubt type (doc the-function-or-macro-name) in REPL and see the documentation right there. I use doc much more often than online docs – it’s always up to date with the version I’m using and it’s already right there under my fingers anyway.

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