mask.clj

(defn get-digit [n]
	(cond
		(nil? n) "_"
		(nil? (re-find #"\d" (str n))) ""
		:else n))

(defn get-char [n]
	(cond
		(nil? n) "_"
		(nil? (re-find #"[A-Za-z]" (str n))) ""
		:else n))

(defn apply-mask [mask input]
	(loop [filteredmask mask i input output ""]
		(let [m (first filteredmask)]
			(cond
				(nil? m) (if (= "" output) i output)
				(= "#" (str m)) (recur (rest filteredmask) (rest i) (str output (get-digit (first i))))
				(= "x" (str m)) (recur (rest filteredmask) (rest i) (str output (get-char (first i))))
				:else (recur (rest filteredmask) i (str output m))))))


(apply-mask "(###) ### ####" "6666666666")