Notes from 10/18/02

- study S-expression representaations and alternate ways of writing

- for tree representations (on the HW) empty list is a problem
	- pick something other than an integer to represent it
	- possibly ()
	- allowing this in the tree itself has interesting implications
		- allows infinitly many representations of a list

- HW is not about representing nested lists
- using nested lists to do the representation

- observe testing style on accumulate_rl
	- good way of testing things
	- shows what was done in a way arithmetic ops do not
- also accumulate_rl gives an interesting way to define concatenate
- quiz problem will be slightly harder than concatenate (but not too much)
- notice that accumulate_lr is iterative (because it can written that way)
- however, rl is recursive (because there's no nice iteration)
	- issue with getting to the back of the list
	- using a last procedure would increase cost
	- so would using (car (reverse list)) because reverse is costly too