Recursive processing of a list is based on a base case (often an empty list), which usually has a simple answer, and a recursive case, whose answer is based on a recursive call to the same function on the rest of the list.
(defun length (lst)
(if (null lst) ; test for base case
0 ; answer for base case
(+ 1
(length (rest lst))) ) ) ; recursive call
public static int length (Cons lst) {
if ( lst == null )
return 0;
else return (1 +
length( rest(lst) )); }