5 Racket Turtle examples with recursion

5.1 Spiral with changing pen color

Spiral created by recursively increasing the distance that turtle moves. Pen colors are changed according to a list of colors.

(define COLORS1 (list "red" "green" "yellow" "purple"))

(define (spiral a x times)

(if (< times 0)

empty

(append (list (forward x)(turn-left a))

(spiral a (+ x 2)(sub1 times)))))

(define spiral-image

(list (change-pen-size 2)

(change-bg-color "black")

(change-color COLORS1)

(spiral 91 1 152)))

5.2 Spiral with changing pen color and size

Spiral created by recursively increasing the distance that turtle moves. Pen colors are changed according to a list of colors and pen size increases each time.

(define COLORS2 (list "red" "blue" "green" "yellow" "purple"))

(define (side x w a)

(list (change-pen-size w)(forward x)(turn-left a)))

(define (spiral2 x w a times)

(if (<= times 0)

empty

(cons (side x w a)

(spiral2 (+ x 5) (+ w 1) a (sub1 times)))))

(define spiral-image2 (list (change-bg-color "black")

(change-color COLORS2)

(spiral2 1 1 45 45)))

5.3 Flower spiral with changing sizes and colors

Flower spiral programmed using the stamper functionality. The colors of the flowers change randomly.

(define (leaf size color)

(ellipse (* 8 size) size "solid" color))

(define (leafs size color)

(overlay (leaf size color)

(rotate 90 (leaf size color))))

(define (draw-flower size color)

(overlay (circle (/ size 2) "solid" "white")

(leafs size color)

(rotate 45 (leafs size color))))

(define (flower-spiral a x times)

(if (< times 0)

empty

(append (list (forward x)(turn-left a))

(flower-spiral a (+ x 6)(sub1 times)))))

(define (draw-flowers n size)

(if (<= n 0)

empty

(cons (rotate size (draw-flower size (make-color (random 255)

(random 255)

(random 255))))

(draw-flowers (sub1 n)(add1 size)))))

(define spiral-image3 (list (stamper-on (draw-flowers 20 1))

(pen-up)

(flower-spiral 25 1 20)))

5.4 Star spiral with changing sizes and colors

Star spiral programmed using the stamper functionality. The colors of the stars change randomly.

(define (draw-stars n size)

(if (<= n 0)

empty

(cons (rotate size (star size "solid" (make-color (random 255)

(random 255)

(random 255))))

(draw-stars (sub1 n)(add1 size)))))

(define spiral-image4 (list (stamper-on (draw-stars 100 1))

(pen-up)

(spiral 91 1 100)))