I have no idea what I am doing

filter.clj

(defn my_even? [n]
  (= 0 (rem n 2)))

(defn my_filter [test_fn input_list]
  
  (defn recstep [remaining_input acc]
    (if (= 0 (count remaining_input))

      acc

      (let  [ next_input  (drop 1 remaining_input)
              this_ele    (first remaining_input)
              next_acc    (if (test_fn this_ele)

                            (concat acc [this_ele])

                            acc)]
        (recstep next_input next_acc))))

  (recstep input_list (list)))

(prn
  (my_filter my_even? (take 10 (range))))
  ; > (0 2 4 6 8)
  ; => nil