FAQ

How do I use Expound to print all spec errors?

Using set!

In most cases, you'll want to use set! to install the Expound printer:

(set! s/*explain-out* expound/printer)

Using alter-var-root

If you using Expound within a REPL, alter-var-root will not install the Expound printer properly - you should use set! as described above.

If you using the Expound printer in a non-REPL environment, set! will only change s/explain-out in the current thread. If your program spawns additional threads (e.g. a web server), you can set s/explain-out for all threads with:

(alter-var-root #'s/*explain-out* (constantly expound/printer))

set! will also not work within an uberjar. Use alter-var-root instead.

Why don't I see Expound errors for instrumentation or macroexpansion errors?

As of clojure.spec.alpha 0.2.176 and ClojureScript 1.10.439 (which contains cljs.spec.alpha), spec no longer includes the spec error in the exception message. Instead, the error will now include more data about the spec error, but this isn't printed by default in older REPLs.

Clojure 1.10.0 updates the REPL to print this new error data. As of this writing, the Clojurescript REPL is in the process of being updated.

To summarize, spec errors will be printed at the REPL with these combinations:

• clojure.spec.alpha 0.2.168 will work with Clojure 1.9.0
• clojure.spec.alpha 0.2.176 will work with Clojure 1.10.0
• Clojurescript 1.10.238 and 1.10.339