Solution to SICP Exercise 1.38

Solution to Exercise 1.38:

(define (cont-frac n d k)
(define (iter i sub-expr)
(if (= i 0)
sub-expr
(iter (- i 1) (/ (n i) (+ (d i) sub-expr)))))
(iter (- k 1) (/ (n k) (d k))))

(define (e k)
(+ (cont-frac (lambda (i) 1.0)
(lambda (i) (if (= (remainder (+ i 1) 3) 0)
(* 2 (/ (+ i 1) 3))
1.0))
k)
2))