(define x 5)
(set! x (+ x 1))
; binds x to 6
x

; no previous binding for y
(set! y 5)
; produces "unbound variable" message

((lambda (x)
  (set! x (+ x 1))
  (set! x (+ x 1))
  x)
 5)
; returns 7
; x should still be bound to the value it had
x

(define a 0)
((lambda (x)
  (set! a (+ x 1))
  (set! x (+ a 1))
  (* a x))
 3)
; rebinds a to 4, then returns 20
; x's binding doesn't change
a
x

(define a 0)
((lambda (a x)
  (set! a (+ x 1))
  (set! x (+ a 1))
  (* a x))
 3 5)
; returns 42
; a should still be bound to 0
a

(define x 0)
((lambda (x)
  (set! x 
    ((lambda (x) 
      (set! x (+ x 1))
      (+ x 1))
     (+ x 1)) )
  (+ x 5))
 x)
; returns 8
; x should still be bound to 0
x

(define a 0)
(define b 10)

(define f 
  (lambda (x a)
    (set! x (+ b 1))
    (set! b (* b 2))
    (g (+ a x)) ) )

(define g
  (lambda (b)
    (set! a 30)
    (+ a b) ) )

(f 3 14)
; returns 55 after rebinding the global a to 30 and the global b to 20
a
b
x