(defn vec-to-num [coll]
  (loop [c (reverse coll)
         result 0]
    (if (seq c)
      (recur (rest c) (+ (* 10 result) (first c)))
      result)))

(defn num-to-vec [num]
  (loop [n num
         result []]
    (if (< n 10)
      (conj result n)
      (recur (quot n 10) (conj result (mod n 10))))))

(defn add-two-numbers [coll1 coll2]
  (num-to-vec (+ (vec-to-num coll1)
                 (vec-to-num coll2))))

The given code defines four functions: vec-to-num, num-to-vec, add-two-numbers, and executes a calculation at the end.

The vec-to-num function takes a collection coll representing a vector of digits and converts it into a number. It does so by iterating over the reversed order of the collection and multiplying each digit by the corresponding power of 10, then summing them up. The result is returned as a number.

The num-to-vec function takes a number num and converts it into a vector of digits. It does so by repeatedly dividing the number by 10 and taking the remainder (modulus) as the digit, until the number becomes less than 10. The digits are accumulated in reverse order and returned as a vector.

The add-two-numbers function takes two collections coll1 and coll2, representing two numbers in reverse order (least significant digit first), and adds them together. It does so by converting both collections to numbers using the vec-to-num function, adding them together, and then converting the result back to a vector using the num-to-vec function.

To test:

(def l1 [2 4 3])
(def l2 [5 6 4]) 

(add-two-numbers l1 l2)
; (= (list->nodes [7 0 8]) 

Finally, the code defines two vectors l1 and l2 representing the numbers [2, 4, 3] and [5, 6, 4], respectively. It then calls the add-two-numbers function with l1 and l2 as arguments, which returns the sum of the two numbers as a vector.

In this case, the sum of [2, 4, 3] and [5, 6, 4] is [7, 0, 8], so the code will output [7, 0, 8].