(def defn
  (mac (name args . body)
    (list 'def name (cons 'fn (cons args body)))))

(defn map-aux (f acc l)
  (if (nil? l)
    (acc f '())
    (map-aux
      f
      (fn (f ys)
        (acc f (cons (f (head l)) ys)))
      (tail l))))

(defn map (f l)
  (map-aux f (fn (f x) x) l))

(println
  (map (fn (x) (* x x))
       '(1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20)))