CSC151 2009F, Class 34: Randomized (Unpredictable) Drawing

Admin:
* Happy belated halloween!
* Are there questions on exam 2?
* Reading for Tuesday: Characters and Strings
* There was enough difficulty on Friday's quiz that I'm not counting it
  * I'm also not returning it today
  * Anyone who did not take it on Friday should take it now
* After discussing the quiz, I'll try to do a quick intro today. (I failed)

Overview:
* About the quiz.
* Random art.
* Why use randomness.
* The random procedure.
* Simulation.

Exam questions
* Question 4: What type should drawings-largest return?  
  * A drawing
* Question 3: Can we make it work with ellipses?
  * Yes
  * Will we get extra credit if we do it correctly?
    * Maybe
  * Will we lose credit if we do it incorrectly?
    * Probably
* Question 5: Can we define turtle-polygon! separately?
  * Yes
  * Can we copy it from the appropriate homework assignment?
    * Yes, provided you cite that homework.
* Question 10: Does it matter that max works with fifteen (or ten or ...)
  elements as well as two?
  * No.
Quiz

(define whatzitdo
  (lambda (vals)
    (and (not (null? vals))
         (or (and (integer? (car vals)) (odd? (car vals)))
             (whatzitdo (cdr vals))))))

* If vals is empty, returns #f
* If vals is a one-element list, (x)
  * If x is an odd integer, returns #t
  * If x is not an odd integer, returns #f
* If vals is a multiple-element list (X stuff)
  * If first element is odd integer, returns #t
  * Otherwise recurses
* So, returns #t if there is an odd element in the list.

Simulate the idea that art can be unpredictable, with limited involvement
from "the artist"

Most languages provide a procedure that gives back "random" (unpredictable)
results

(random N) = > a number between 0 and N-1

(define count-from
  (lambda (lower upper)
    (let kernel ((position lower))
      (if ______________
          (list upper)
          (cons (position (kernel _____________)))))))