match fn

match.clj

(defn match [pattern input-string]
  (loop [[[op op-arg alt] :as pattern] pattern [chr :as input-string] input-string]
    (if op
      (let [res (case op
                  :req (= op-arg chr)
                  :opt (if (= op-arg chr)
                         true
                         :next)
                  :alt (or (= op-arg chr)
                           (= alt chr)))]
        (and res (recur (rest pattern) (if (= res :next)
                                         input-string
                                         (rest input-string)))))
      (not chr))))