1. lexical depth
------------------------------------------
	  LEXICAL DEPTH

def: the lexical depth of a variable use
     is



 !-----------------------------!
 !   (lambda (x)	       !
 !   !----------------------!  !
 !   ! (lambda (y)	    !  !
 !   !  		    !  !
 !   !    (car (cons x y)) )!) !
 !   !----------------------!  !
 !-----------------------------!



------------------------------------------
	What's the lexical depth of y? x? cons? car?
  2. lexical address
------------------------------------------
	  LEXICAL ADDRESS

identify each varref by 2 numbers:
	d = lexical depth
	p = position, counted from 0

format:
	(v : d p)
         ^
         \-------- var name

(lexical-address
 (parse-expression 'cdr)) ==> (cdr : 0 0)

(lexical-address
 (parse-expression
     '(lambda (ls) (cdr ls))))
  ==> (lambda (ls)
       ((cdr : 1 0) (ls: 0 0)))

(lexical-address
 (parse-expression
     '(lambda (x)
        (lambda (y)
        (car (cons x y))))))
  ==> (lambda (x)
        (lambda (y)
	  ((car :   ) ((cons :   )
                          (x :    )
			  (y :    )))))
------------------------------------------
------------------------------------------
	  FOR YOU TO DO

What is?...

(lexical-address
 (parse-expression 
  '(lambda (x) (lambda (y) x))))


(lexical-address
 (parse-expression 
  '(lambda (x) (lambda (x) x))))


(lexical-address
 (parse-expression 
  '(lambda (x) (lambda (z) x))))


(lexical-address
 (parse-expression 
   '(lambda (a b c)
      (lambda (f g)
        (f (g a b) c a)))))





------------------------------------------
  3. renaming variables (skip)
	do variable names really matter to a compiler?
------------------------------------------
	   RENAMING FORMALS

Which are equivalent?

 (lambda (x) (lambda (y) x))  ; a

 (lambda (x) (lambda (x) x))  ; b

 (lambda (x) (lambda (z) x))  ; c

 (lambda (m) (lambda (y) m))  ; d

 (lambda (m) (lambda (y) x))  ; e


Problems in renaming variables:
   - capture, as in

   - respecting inner bindings, as in

------------------------------------------
	What are their lexical address forms?
------------------------------------------
	FOR YOU TO DO

Are these equivalent?

  (lambda (x)
    ((lambda (x) (cons x '()))
     (cons x '())))

and
 
  (lambda (y)
    ((lambda (x) (cons y '()))
     (cons y '())))

------------------------------------------