Scheme Turtle

<eval> (clear canvas) (move turtle 100 100)</eval>

(penwidth turtle 5) (pencolor turtle 255 0 0) (forward turtle 50) (right turtle 90) (forward turtle 50) (right turtle 90) (pencolor turtle 0 0 255) (forward turtle 50) (right turtle 90) (forward turtle 50)

(define t (clone turtle)) (forward t 50)

<eval> (clear canvas2) (move turtle2 200 200)</eval>

(define tree

(lambda(side) 
 (cond [(< side 2) #t] 
       [else  
         (penwidth turtle2 (/ side 10))    
         (forward turtle2 side)  
         (left turtle2 45)  
         (tree(/ side 2))  
         (right turtle2 90)  
         (tree(/ side 2))  
         (left turtle2 45)  
         (backward turtle2 side)])))

(tree 100)

<eval> (clear canvas3) (move turtle3 200 200)</eval>

(define tree

(lambda(side) 
 (cond [(< side 2) #t] 
       [else  
         (penwidth turtle3 (/ side 10))    
         (forward turtle3 side)  
         (left turtle3 45)  
         (tree(/ side 2))  
         (right turtle3 90)  
         (tree(/ side 2))  
         (left turtle3 45)  
         (backward turtle3 side)])))

(tree 100)

Zur Erforschung echter Rekursion verwenden wir die Prozedur random-walk.

<eval> (clear canvas4) (move turtle4 200 200)</eval>

(define random-walk

 (lambda (angle length n turtle)
   (if (= n 0)
       (send turtle pen-erase!)
       (begin          
         (send turtle forward! length)
         (send turtle right! angle)
         (random-way (+ 5 (random angle))(+ 5 (random length)) (- n 1) turtle)
         (sleep-for-a-while 0.01)
         (send turtle left! angle)
         (send turtle backward! length)))))

(random-way 360 20 50 turtle4)