fold-left.scm

(define (fold-left op initial sequence)
  (define (iter result rest)
    (if (null? rest)
	result
	(iter (op result (car rest))
	      (cdr rest))))
  (iter initial sequence))
(define fold-right accumulate)

(define (reverse seq)
  (fold-right (lambda (x y) (append y (list x))) '() seq))
(define (reverse seq)
  (fold-left (lambda (x y) (cons y x)) '() seq))