Find the approximation of pi

pi.scm

(define (pi-iter i max sum)
  (if (= i max)
     (* 4 sum)
     (let ((k (/
                            (^ (- 1) i)
                            (+ (* 2 i) 1))))
     (pi-iter (+ i 1) max (+
                           sum
                           k)))
     ))


(define (^ x y)
    (cond ((= y 0) 1)
          ((= y 1) x)
          (else (^-iter x 1 y x)))
  )

(define (^-iter x i max result)
(if (= i max) result
   (^-iter x (+ i 1) max (* x result))
))

(display "pi的近似值：")
(display (pi-iter 0 50000 0))
(newline)