Add two numbers presented as two lists, an exercise in Lisp-cn google group. See https://groups.google.com/forum/#!topic/lisp-cn/AVEjxh0A5r0

gistfile1.scm

(define (list-add lst1 lst2)
  (define (iter a1 a2 carry ret)
    (cond ((and (null? a1) (null? a2))
           (if carry
               (append ret '(1))
               ret))
          ((null? a1)
           (if carry
               (iter '(1) a2 #f ret)
               (append ret a2)))
          ((null? a2)
           (if carry
               (iter a1 '(1) #f ret)
               (append ret a1)))
          (else (let ((r (+ (car a1)
                            (car a2)
                            (if carry 1 0))))
                  (if (>= r 10)
                      (iter (cdr a1)
                            (cdr a2)
                            #t
                            (append ret (list (- r 10))))
                      (iter (cdr a1)
                            (cdr a2)
                            #f
                            (append ret (list r))))))))
  (iter lst1 lst2 #f '()))