Impure function detectio

pure.clj

;; If you name your impure functions with a name ending in "!",
;; you can use this handy macro to check if a form uses any impure functions.

(declare find-impure)

(defn ends-in-bang? [s]
  (= \! (last (str s))))

(defn impure? [e]
  (cond
    (seq? e) (find-impure e)
    (symbol? e) (when (ends-in-bang? e)
                  e)
    :else nil))

(defn find-impure [coll]
  (when-let [s (seq coll)]
    (lazy-seq
      (cons
        (impure? (first s))
        (find-impure (rest s))))))

(defmacro pure [e]
  (let [i (find-impure e)
        impures (set (filter identity (flatten i)))]
    (when (seq impures)
      (str "Impure functions detected: "
           (apply str (interpose " - " impures))))))

;; Example

(pure (if (= 1 2)
        (yiss! 1 2 3)
        false))

;; =>  Impure functions detected: yiss!