A Simple Turtle Graphics Implementation in Clojure

Turtle graphics is a popular way of introducing programming to kids. It was part of the original Logo programming language developed by Wally Feurzig and Seymour Papert in 1966. Turtle, originally a robotic creature moves on the floor. It takes commands relative to its own position, such as "move forward 10 steps" and "turn left 90 degrees". Turtle also has a pen which may be lowered to the floor so that a trace is left of where it has traveled.

turtle.clj

(defn fib [turtle depth]
  (forward turtle 30)
  (if (> depth 2)
    (do 
      (left turtle 15)
      (fib turtle (- depth 1))
      (right turtle 30)
      (fib turtle (- depth 2))
      (left turtle 15)))
  (back turtle 30))

(let [turtle (turtle 400 400)]
  (pen-up turtle)
  (go turtle 0 -100)
  (pen-down turtle)
  (fib turtle 10)
  (show turtle))

$fractal fern$

(defn fern [turtle size]
  (if (> size 4)
    (do 
      (forward turtle  (/ size 25))
      (left turtle 90) (fern turtle (* size 0.3))
      (right turtle 90)
      (right turtle 90) (fern turtle (* size 0.3))
      (left turtle 90)  (fern turtle (* size 0.85))
      (back turtle (/ size 25)))))

(let [turtle (turtle 400 400)] 
  (pen-up turtle)
  (go turtle 0 -200)
  (pen-down turtle)
  (pen-color turtle Color/green)
  (fern turtle 1500)
  (write turtle "test.png"))

$fractal tree$