1 (defun ripple-carry-adder (la lb ls c)
2   (let ((n (length la)))
3     (unless (= n (length lb) (length ls))
4       (error "Expecting all lists of same length"))
5     (labels ((ripple-build (la lb lcin ls lcout)
6 	       (unless (null la)
7 		 (full-adder (car la) (car lb) (car lcin)
8 			     (car ls) (car lcout))
9 		 (ripple-build (cdr la) (cdr lb) (cdr lcin)
10 			       (cdr ls) (cdr lcout)))))