Notes from 10/25/02

- survey of issues about variable scope
	- (let ((v1 e1) ... (vn en)) body)
		- scope of all v1 .. vn is body only
		- this rules out recursive procedures
		- e1 is not in the scope of v1
	
	- (letrec ...
		- alternate form
		- scope of v1 ... vn includes body AND all e1 ... en
		- allows recursion, and mutual recursion

	- these two do not change values of variables, but introduce new ones
	- note: outside variables w/ same name will be inaccesible within a let

	- (lambda (v1 ... vn) body)
		- scope is body
		- does it without establishing bindings - those are introduced later, upon application

	- note: the first let form is the same as ((lambda (v1 ... vn) body) e1 ... en)
	- letrec is possible to do, but much much harder as lambda
	- subtle point: scope in lambda is for that evaluation of the function; let is for all

	- (define v1 body)
		- scope of v1 is body, and whatever follows the define
		- if define is in an internal structure, the end of that structure is also the end of scope for the define
		- can have nasty rules when related to functions
		- earlier values matter for non-procedures, and don't matter for procedures

	- (define (f x1 ... xn) body)
		- scope of f is body and following
		- scope of variables is like lambda: body and not what follows

	- problem with lambda and substitution is called:
		"capture of a free variable"