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 _____________)))))))