1.2.4-fast-expt.rkt

#lang sicp
(define (fast-expt b n)
  (cond ((= n 0) 1)
    ((even? n) (square (fast-expt b (/ n 2))))
    (else (* b (fast-expt b (- n 1))))))

(define (even? n)
  (= (remainder n 2) 0))

(define (square n) (* n n))