How instrumentation works.clj

(defn hi [name] (println "hello " name))

(s/def ::hi-args (s/cat :name string?))

(def registry {`hi ::hi-args})

(defn instrument []
  (s/check-asserts true)
  (for [[sym spec] registry]
    (alter-var-root (find-var sym)
                    (fn [f]
                      (fn [& args]
                        (s/assert spec args)
                        (apply f args))))))

(instrument)

(hi 3)