Set as Linked List

A linked list can be used as a representation of a set. member (written ∈) tests whether a given item is an element of the list. member returns the remainder of the list beginning with the desired element, although usually member is used as a predicate to test whether the element is present or not.

(member 'dick '(tom dick harry))   ->  (dick harry)

(member 'fred '(tom dick harry))   ->  nil

public static Cons member (Object item, Cons lst) {
  if ( lst == null )
     return null;
   else if ( item.equals(first(lst)) )
           return lst;
         else return member(item, rest(lst)); }

(defun member (item lst)
  (if (null lst)
      nil
      (if (eql item (first lst))
          lst
          (member item (rest lst)) ) ) )