l99

(defn my-last [xs]
  (cond
    (empty? (rest xs)) (first xs)
    :otherwise (recur (rest xs))))
(println
  (my-last '(a b c d)))

(defn my-but-last [xs]
  (cond
    (empty? (rest (rest xs))) xs
    :otherwise (recur (rest xs))))
(println
  (my-but-last '(a b c d)))

(defn element-at [xs n]
  (cond
    (empty? xs) "failed"
    (= n 1) (first xs)
    :otherwise (recur (rest xs) (- n 1))))
(println
  (element-at '(a b c d e) 3))

(defn length [xs]
  (defn length2 [xs n]
    (cond
      (empty? xs) n
      :otherwise (recur (rest xs) (+ n 1))))
  (length2 xs 0))
(println
  (length '(a b c d e)))

(defn my-reverse [xs]
  (defn reverse2 [xs ys]
    (cond
      (empty? xs) ys
      ;:otherwise (recur (rest xs) (cons (first xs) ys))))
       :otherwise (recur (rest xs) (conj ys (first xs)))))
  (reverse2 xs '()))
(println
  (my-reverse '(a b c d e)))

(defn palindrome? [xs]
  (= xs (my-reverse xs)))
(println
  (palindrome? '(a b c d e)))
(println
  (palindrome? '(a b c b a)))

(defn my-flatten [xs]
  (cond
    (list? (first xs)) 
    :otherwise 2))
(println
  (my-flatten '((a b) c (d (e)))))