gistfile1.clj

(ns calc (:gen-class))

(defmulti calc (fn [t] (if (seq? t) (first t) :num)))

(defn def-prefix-op [sym f]
  (defmethod calc sym [[op & args]] (apply f (map calc args))))

(doseq [[sym op] [['+ +] ['- -]
                  ['* *] ['/ /]
                  ['sin #(Math/sin %)]]]
  (def-prefix-op sym op))

(defmethod calc :num [n] n)

(defn -main []
  (letfn [(prompt [] (print "=>") (flush) (read-line))]
    (println (calc (read-string (prompt)))))
  (recur))