Untying the Recursive Knot

fact'.clj

(defn fact' [fact n]
  (if (= n 0) 1
      (* n (fact (dec n)))))

fact.clj

(defn fact [n]
  (if (= n 0) 1
      (* n (fact (dec n)))))

odd'-even'.clj

(defn even' [odd es os [e & t]]
  (if e 
    (odd (conj es e) os t)
    [es os]))

(defn odd' [even es os [o & t]]
  (if o
    (even es (conj os o) t)
    [es os]))

odd-even-y.clj

(y (fn [f & args] (apply even' (partial odd' f) args)) [] [] (range 7))
;; [[0 2 4 6] [1 3 5]]

odd-even.clj

(declare odd)

(defn even [es os [e & xs]]
  (if e
    (odd (conj es e) os xs)
    [es os]))

(defn odd [es os [o & xs]]
  (if o
    (even es (conj os o) xs)
    [es os]))

(even [] [] (range 7))
;; [[0 2 4 6] [1 3 5]]

odd-event.clj

(declare odd)

(defn even [es os [e & xs]]
  (if e
    (odd (conj es e) os xs)
    [es os]))

(defn odd [es os [o & xs]]
  (if o
    (even es (conj os o) xs)
    [es os]))

(even [] [] (range 7))
;; [[0 2 4 6] [1 3 5]]

y-comb.clj

(defn y [f & xs]
  (apply f (partial y f) xs))

y-fact-extra.clj

(y (fn [f n]
     (println "fact" n)
     (fact' f n))
   5)
;; fact 5
;; fact 4
;; fact 3
;; fact 2
;; fact 1
;; fact 0
;; 120

y-fact.clj

(y fact' 10)
;; 3628800