;; Strings are immutable: a character cannot be assigned in place
(def text "1-3-2")

;; Work on a vector of characters and glue it back
(def fixed
  (apply str (-> (vec text)
                 (assoc 2 \2)
                 (assoc 4 \3))))
;; fixed is "1-2-3"

(println "text is" text)
(println "fixed is" fixed)