CSC151 2007S, Class 15: Representing Images as Lists of Spots

Admin:
* Sorry for the problems with DrFu over the weekend.  We're hoping not too many more crop up.
  * Free extension on exam until class time on Monday Oct 1
  * The charge for an extension beyond that time is 100 points on the test, even if you work eight or more hours on the test
* Warning! For those of you who did the reading early: I've changed terminology slightly.
* New groups!  Sam used a naive technique for making these pairs.
* Reading for Tuesday: Iterating Over Lists.
* Are there questions on Exam 1?
* SENTIENT AND MALICIOUS

Overview:
* Spot lists: Another perspective on images.
* Lists in Scheme.
* Basic list operations.
* Processing spot lists.

/Ways to Represent Collections in Scheme/

* The most common technique: The list
* Core part of Lisp, the language that Scheme was based on
* In the abstract, a list is an ordered collection of data
* In the concrete, we need procedrues to work with lists
  * nil, the name of the empty list
  * (cons value lst) - Add value to the front
    * Backwards: We traditionally add to the end.
  * (car lst) - first element
  * (cdr lst) - all but first element
  * (list val1 val2 ... valn) - create a list of val1 ... valn
    * In that order!

/Debrief/

* Sam's typoes are really tests to see if you're paying attention.
*