CSC151 2009F, Class 24: Revisiting Lists

Admin:
* Reading for Friday: Recursion 
  * Yet another way to do repetition
* A few problems on the homework were a bit more difficult than 
  we anticipated.  
  * I apologize.  
  * However, I think you're probably now a bit better with building 
    anonymous procedures, and I think that's a good thing.
* Friday's quiz will include 
  * conditionals (Friday and Monday)
  * image-compute (yesterday) 
  * The new list operations, like cons, car, and cdr (today)
  * Make sure you understand exercise 3 from yesterday and 5e from today.
  * Make sure that you're comfortable with the new list operations.
* Assignment 6 is now ready, and is due Wednesday of next week.
  * We'll talk about it after we get through the administrivia
* Looking ahead: No large assignment will be due the week after break.
* Looking further ahead: GIMP (the other one) presents Rent (Nov. 13-15).
* Two things you should know about GIMP+MediaScript
  * How to close a lot of open windows
  * How to insert the Six P's.

Overview
* About the new assignment
* Lists, Revisited
* New List Operations
* Drawings as Values

Lists
* A collection of values
  * Homogeneous - All the same type of thinga
  * With for-each, map - Basically, for iteration
* There's more to lists in Scheme
  * Heterogeneous - Different types of values
  * Use for other purposes, such as storing lots of information about a
    drawing
* Need more ways to work with the elements in a list
  * (list-ref lst pos) - Grab an element
  * (car lst) - Grab the first element
  * (cdr lst) - Drop the first element
  * (cons value lst) - Create a new list by adding an element to the front
  * null - the empty list