Notes from 10/14/02

- main discrepancy between older lisp and Scheme
	- atom(?) is in Lisp but not Scheme
	- Scheme has number?, symbol? etc
	- this is because Scheme doesn't want you bundling everything other than lists together
	- (not (pair? x)) is the bad way to simulate atom? in Scheme
		- eventually this will become very bad
	- another issue is whether () is an atom or not

- tree sum example
	- specific one gets redefined in terms of general abstract function

- naming said general function
	- the sum version appears to evaluate the sexpr with + at the nodes
	- so call this general one eval_sexpr

- side note on difference between ' and (list ...)

- eventually you will want more than binary trees and nested lists
	- trees let you represent lots of different kinds of information
	- what you take as basic changes your idea of combining forms, etc.
	
	- problem, for example:
		- (+ 1 2 (* 2 3 4))
		- this doesn't have the same label (operation) on each node
	- it is possible to eval this like we did in eval_sexpr
	- gets very very ugly though

	- right way to do it is to think of it like a nested list/non-binary tree even though underneath we know that it isn't

- this whole deal is called data abstraction