(defn red [len]
  (* (+ 0.5 (* 0.1 (rand-int 5))) len))

(defn col [len]
  (if (< len 10) "green" "brown"))

(defn ang []
  (+ 10 (rand-int 45)))

(defn tree [len]
  (when (>  len 2)
    (set-pen-color (col len))
    (forward len)
    (let [a1 (ang) a2 (ang)]
      (left a1)
      (tree (red len))
      (right (+ a1 a2))
      (tree (red len))
      (left a2))
    (set-pen-color (col len))
    (forward (- len))))

(reset)
(set-speed nil)
(left 90)
(pen-up) (forward -150) (pen-down)
(tree 100)
