recursive_function.clj

(defn sum [xs]
  (let [f (fn f [acc xs]
            (if (empty? xs)
              acc
              (recur (+ acc (first xs)) (rest xs))))]
    (f 0 xs)))

(sum '(1 2 3))  ; => 6


(defn sum* [xs]
  (letfn [(f [acc xs]
            (if (empty? xs)
              acc
              (recur (+ acc (first xs)) (rest xs))))]
    (f 0 xs)))

(sum* '(1 2 3))  ; => 6


(defn sum** [xs]
  (loop [acc 0
         xs xs]
    (if (empty? xs)
      acc
      (recur (+ acc (first xs)) (rest xs)))))

(sum** '(1 2 3))  ; => 6

recursive_function.scm

(define (sum xs)
  (letrec ((f (lambda (acc xs)
                (if (null? xs)
                    acc
                    (f (+ acc (car xs)) (cdr xs))))))
    (f 0 xs)))

(sum '(1 2 3))  ; => 6


(define (sum* xs)
  (define (f acc xs)
    (if (null? xs)
        acc
        (f (+ acc (car xs)) (cdr xs))))
  (f 0 xs))

(sum* '(1 2 3))  ; => 6