(define (s)
  (append (np) (vp)))

(define (np)
  (case (random 2)
    ((0) (pn))
    ((1) (append (det) (cn)))))

(define (pn)
  (case (random 6)
    ((0) '(john))
    ((1) '(mary))
    ((2) '(frog))
    ((3) '(toad))
    ((4) '(alice))
    ((5) '(bob))))

(define (det)
  (case (random 4)
    ((0) '(a))
    ((1) '(the))
    ((2) '(every))
    ((3) (append (np) '(s)))))

(define (cn)
  (case (random 4)
    ((0) '(cake))
    ((1) '(ball))
    ((2) '(book))
    ((3) (append (adj) (cn)))))

(define (adj)
  (case (random 3)
    ((0) '(beautiful))
    ((1) '(big))
    ((2) (append '(very) (adj)))))

(define (vp)
  (case (random 2)
    ((0) (iv))
    ((1) (append (tv) (np)))))

(define (iv)
  (case (random 4)
    ((0) '(slept))
    ((1) '(ate))
    ((2) '(shined))
    ((3) '(smelled))))

(define (tv)
  (case (random 4)
    ((0) '(made))
    ((1) '(ate))
    ((2) '(saw))
    ((3) '(smelled))))