sicp-exs/sicp-ex-1.16.rkt

(define (sqr n)
  (* n n))

(define (fast-ext-iter number power product)
  (cond ((= power 0) product)
        ((even? power) (fast-ext-iter (sqr number)
                                      (/ power 2)
                                      product))
        (else (fast-ext-iter number
                             (- power 1)
                             (* number product)))))

(define (fast-ext number power)
  (fast-ext-iter number power 1))

(fast-ext 2 5)