This works:
(+ 1 2 3)
6
This doesn't work:
(+ '(1 2 3))
This works if 'cl-*' is loaded:
(reduce '+ '(1 2 3))
6
If reduce were always available I could write:
(defun sum (L)
(reduce '+ L))
(sum '(1 2 3))
6
What is the best practice for defining functions such as sum?