Return items of a list in Lisp -

i have write program in lisp returns first item of list if contains number of elements, , last if contains odd number of elements. need little advice on start? don't need whole program.

you can length of list length.

(length '(a b c)) ;; 3 

you can go , check number against predicate function evenp, returns t or nil depending on if argument or not.

(evenp 1) ;; nil (evenp 2) ;; t 

the function first returns first element of list.

(first '(a b c)) ;; 

the function last returns last cons of list, you'll have unwrap value using first.

(last '(a b c)) ;; (c) (first (last '(a b c))) ;; c 

you combine these function so:

(defun get-first-if-even-length (list)   (if (evenp (length list))       (first list)     (first (last list)))) 

this function returns first or last element in list, depending if length or not.