;; compute the nth Fibonacci number,
;; where n is non-negative
(define f
  (lambda (n)
    (if (< n 2)
        n
        (+ (f (- n 1))
           (f (- n 2))))))

;; compute n! for nonnegative integer n
(define factorial
  (lambda (n)
      (do ((i 1 (+ i 1))
           (fact 1 (* fact i)))
        ((> i n) fact))))

; original from concabs p387
(define from-to-do
  (lambda (start stop body)
    (if (> start stop)
        'done
        (begin (body start)
               (from-to-do (+ 1 start) stop body)))))

;; our version using do
(define my-from-to-do
  (lambda (start stop body)
    (do ((i start (+ i 1)))
      ((> i stop) 'done)
      (body i))))

; original from concabs p416
(define from-to-add
  (lambda (start end f)
    (if (> start end)
        0
        (+ (f start)
           (from-to-add (+ start 1) end f)))))

;; our version using do
(define my-from-to-add
  (lambda (start end f)
     (do ((i start (+ i 1))
          (sum 0 (+ sum (f i))))
       ((> i end) sum))))