Continuation-passing style

cps.clj

; calculate the sum of odd numbers, the product of even ones and a list of the odds
; example extracted from the book "The Little Schemer"
; more info here http://stackoverflow.com/questions/10692449/the-little-schemer-evens-onlyco
(defn evens-only*&co [l col]
  (cond
   (empty? l) (col `() 1 0)
   (number? (first l))
   (cond
    (even? (first l)) (evens-only*&co
                       (rest l)
                       (fn [newl product sum]
                         (col (cons (first l) newl)
                              (* (first l) product) sum)))
    :else (evens-only*&co
           (rest l)
           (fn [newl product sum]
             (col newl product (+ (first l) sum)))))
   :else (evens-only*&co
          (first l)
          (fn [newl product sum]
            (evens-only*&co (rest l)
                            (fn [dnewl dproduct dsum]
                              (col (cons newl dnewl)
                                   (* product dproduct)
                                   (+ sum dsum))))))))

; collector, how to build the results
(def the-last-friend
  (fn [newl product sum]
    (cons sum (cons product newl))))

(evens-only*&co `(1 (1 1 2) 2 1 3 2) the-last-friend)
; (7 8 (2) 2 2)