CSC151 2007S, Class 35: Naming Local Procedures

Admin:
* EC: This Thursday's talk on scripting video.
  * Snacks at 4:15 in the CS Commons
  * Talk at 4:30 in 3821
* Are there questions on the exam?
* Reading for tomorrow: Characters and Strings.

Overview:
* Why have local procedures.
* Creating local procedures.

=Exam Questions=

Q: Why are you adding something to the cdr of a list?  I thought you
   could't add lists.
   (+ (cdr p) (- 1 x))
A: It's a subtlety of Scheme that we've only covered implicitly.  There's
   now an alternative version available.

Q: Why doesn't my code work?
A: Most typical reason: Difficulty getting the format of cond right.
   (cond
     (TEST CONSEQUENT)
     (TEST CONSEQUENT))
   We've been using cond rather than if to sequence operations
   (cond
     ((should-we-continue? some-info)a
      (update-the-drawing!)
      (recurse!)))

Q: Doesn't cond need an else?
A: It's good to have an else, but it's not required.

=Lab Observations=

You may find the following procedure useful

(define all-rgb?
  (lambda (lst)
    (or (null? lst)
        (and (rgb? (car lst))
             (all-rgb? (cdr lst))))))