CSC297.Java 2003F, Class 15: Lists, Revisited

Admin:
* To copy your files to MathLAN, ftp to ftp.cs.grinnell.edu
* How did the histogram assignment go?
  * Alex thinks he did it.  As does Yvonne
  * Sam compliments Yvonne.  Yes, Sam actually complimented someone.  It happens so rarely.
* How did the "use previous version of the list" trick go?

Overview:
* Review of "use previous version"
  * Almost every list has a link to its cdr.
  * When you need the cdr, you just follow the link.
  * This technique is significantly faster for finding the cdr, and only marginally slower for adding something to the front.
  * Can we use a similar technique to make it faster to add something to the front?
* Building lists with Cons cells
  * Think about each list as containing only two values:
    * The car
    * The cdr
  * To add something to the front, make a new list whose car is the new value and whose cdr is the old list.
  * To find the cdr, just use the old list (as we did before).
* Problem: How to we build an empty list?
  * Solution: New class: EmptyList