Sigma Lisp
?>: (set-implicit 'ar (fn (a i) (if _ (ar-set! a i (car _)) (ar-get a i))))
-> <OBJ:func@[82783D8]>
?>: (local a (array 'a 'b 'c 'd))
-> (a b c d)
?>: (a 1)
-> b
?>: (a 1 'e)
-> e
?>: a
-> (a e c d)