`set!` will apply to threads created within REPL

gistfile1.txt

> clj -Sdeps '{:deps {expound {:mvn/version "0.7.1"}}}'
Clojure 1.9.0
user=> (require '[expound.alpha :as expound] '[clojure.spec.alpha :as s])
nil
user=> ;; default printer is used
user=> (future (s/explain int? "a"))
val: "a" fails predicate: :clojure.spec.alpha/unknown
#object[clojure.core$future_call$reify__8097 0x99a65d3 {:status :ready, :val nil}]
user=> (set! s/*explain-out* expound/printer)
#object[expound.alpha$printer 0x4ad4936c "expound.alpha$printer@4ad4936c"]
user=> ;; Now expound is used in thread
user=> (future (s/explain int? "a"))
#object[clojure.core$future_call$reify__8097 0x25cc7470 {:status :pending, :val nil}]
user=>
-- Spec failed --------------------

  "a"

should satisfy

  int?

-------------------------
Detected 1 error