> (define x 2)
> x
2
> (define x 3)
> x
3
> (set! x 4)
> x
4
> ((n+ 2) 3)
5
> ((n+ 2) 3)
6
> ((n+ 2) 3)
6
> ((n+ 2) 3)
6
> (define 2+ (n+ 2))
> (2+ 2)
5
> (2+ 2)
6
> (2+ 2)
7
> (define 2+ (n+ 2))
> (2+ 2)
[image] [image] n: undefined;
 cannot use before initialization
> (define p (cons 2 3))
> p
(2 . 3)
> (set-car! p 20)
> p
(20 . 3)
> (set-cdr! p 30)
> p
(20 . 30)
> 
> (define 2+ (n+ 2))
> (n+ 2)
#<procedure:...scheme/mutation.scm:2:2>
> (define 2+ (n+ 2))
> (2+ 2)
n = 3
5
> (2+ 2)
n = 4
6
> (2+ 2)
n = 5
7
> (2+ 2)
n = 6
8
> (2+ 2)
n = 7
9
> (set! xxx 22)
[image] [image] set!: assignment disallowed;
 cannot set variable before its definition
  variable: xxx
> (sum 5)
5
> (sum 10)
15
> (sum 10)
25
> (define acct (make-account 100))
> (acct 50)
150
> (acct 30)
180
> (acct -110)
70
> (acct -110)
Insufficient funds!
> (acct -110)
Insufficient funds!
> (acct 20)
90
> (define p '(7 5 3))
> (set-cdr! (cdr p) p)
> p
#0=(7 5 . #0#)
> (length p)
[image] [image] user break