CSC151, Class 36: Algorithmic Art

Overview:
* Discussion of exam 2
* More on circles
* About images
* Algorithmically generating and modifying images
* Lab

Notes:
* Admitted students may be visiting.
* How should we structure today's class?
* Questions and answers on exam 2.

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Question 2: in-tree?

DONT' WRITE DOCUMENTATION

Remember that a tree is either (1) a non-pair value or
(2) a pair of two trees.  That recursive data structure
definition should help you write procedures that do things
with trees.

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Question 3: list-of-integers->string

DON'T WRITE DOCUMENTATION

Number of approaches.

One good one: Don't worry about the parens.
Then worry about the parens.

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Question 4: Ugly code

YES, YOU HAVE TO DOCUMENT

How should you approach

(define r
  (lambda (l p?)
    (letrec ((c (lambda (p v)
                  (let ((x (if (p? v) 1 0)))
                    (cons (+ (car p) x) (+ (cdr p) (- 1 x))))))
             (r (lambda (q m)
                  (if (null? m) 
                      (/ (car q) (cdr q))
                      (r (c q (car m)) (cdr m))))))
      (r (cons 0 0) l))))

* Determine the types of the parameters.
* Try some sample calls to see if they reveal clues.
* Figure out more types.
* Gradually expand the parts you can tell about.

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