This works:
(+ 1 2 3) 6
This doesn\'t work:
(+ \'(1 2 3))
This works if \'cl-*\' is loaded:
cl-*
If you manipulate lists and write functional code in Emacs, install dash.el library. Then you could use its -sum function:
(-sum '(1 2 3 4 5)) ; => 15