Mapreduce in Clojure

(defn mapreduce [mapfn reducefn lst]
  (let [rawresult (mapcat mapfn lst)]
    (let [sorted
           (sort (fn [x y]
                   (compare (first x) (first y)))
                 rawresult)]
      (let [keyvals (combinekeys sorted)]
        (map (fn [lst]
               (list (first lst)
                     (apply reducefn (rest lst))))
             keyvals) ) ) ) )


>(mapreduce identity + '(((a 3) (b 2) (c 1))
                         ((b 7) (d 3) (c 5))))

((D 3) (C 6) (B 9) (A 3))