;; Solution for HW6
;; CS3520, Fall 2001
 
(define (ex1 v1 v2)
  (let ([f (let ([x 1]) ;; remembered by f
	     (lambda (y)
	       (begin
		 (set! x (* x y))
		 x)))])
    (begin
      (f v1)
      (f v2))))

(define (ex2 v1 v2)
  (let ([mk (lambda ()
	      (let ([x 1]) ;; not shared by f & g
		(lambda (y)
		  (begin
		    (set! x (* x y))
		    x))))])
    (let ([f (mk)]
	  [g (mk)])
      (begin
	(g v1)
	(f v2)
	(g 1)))))

(define (ex3 v1 v2)
  (let ([mk (let ([x 1]) ;; shared by f & g
	      (lambda ()
		(lambda (y)
		  (begin
		    (set! x (* x y))
		    x))))])
    (let ([f (mk)]
	  [g (mk)])
      (begin
	(f v1)
	(g v2)
	(g 1)))))

(define (ex4 v1 v2 v3 v4)
  (let ([mk (let ([x 1]) ;; shared
	      (lambda ()
		(let ([z 1]) ;; not shared
		  (lambda (y w)
		    (begin
		      (set! x (* x w))
		      (set! z (* z y))
		      (* z x))))))])
    (let ([f (mk)]
	  [g (mk)])
      (begin
	(f v1 v2)
	(g v3 v4)
	(list (f 1 1) (g 1 1))))))