Insert a new element at the N-th position of a list

Question

Is it possible to insert a new element at the N-th position of a list without conj?

defn insert-at [x xs n]
  (let [[before after] (my-drop xs (dec n))]
    (if (empty? after)
      (if (= (count before) (dec n))
        (concat before (replicate 1 x))
        before)
      (concat before (conj after x)))))

Answer 1

Use split-at and insert new element between two halves of list:

(defn list-insert [lst elem index]
  (let [[l r] (split-at index lst)]
    (concat l [elem] r)))

Examples:

(list-insert '(1 2 3 4 5) 0 0)
=> (0 1 2 3 4 5)
(list-insert '(1 2 3 4 5) 1 1)
=> (1 1 2 3 4 5)