exponential_weighted_smooth.clj

(defn exponential-smooth-recur
  [x f]
  (letfn [(smoothed-val [m n f]
    (+ 
      (* m (- 1 f))
      (* n f)))]
    (reverse (lazy-seq
      (loop [observed (rest x) smoothed (list (first x))]
        (if (empty? observed)
          smoothed
          (recur (rest observed) (cons (smoothed-val (first smoothed) (first observed) f) smoothed))))))))

(println (exponential-smooth-recur '(1 2 3 4) 0.9))

(defn exponential-smooth-partial
  [x f]
  (letfn [
    (smooth
      [alpha st xt]
      (conj st
        (+
          (* alpha xt)
          (* (- 1 alpha) (last st)))))]
    (reduce (partial smooth f) [(first x)] (rest x))))

(println (exponential-smooth-partial '(1 2 3 4) 0.9))