gistfile1.txt

(def ops
  {"+" +
   "-" -
   "*" *
   ":" /})

;; calc request handler and proof the app's in clojure jerk
(defn calc [req]
  (let [a (Integer. (get-in req [:route-params :a]))
        b (Integer. (get-in req [:route-params :b]))
        op (get-in req [:route-params :op])
        f (get ops op)]
    (if f
     {:status 200
      :body (str (f a b))
      :headers {}}
     {:status 404
      :body (str "Unknown operator: " op)
      :headers {}})))