The 'eval' function evaluates the 'expression' and returns the resulting value.
(eval '(+ 2 2))            ; returns 4
(eval (cons '+ '(2 2 2)))  ; returns 6
(eval (list '+ '2 '3 ))    ; returns 5
(setq a 10)                ; set up A with value 10
(setq b 220)               ; set up B with value 220
(eval (list '+ a b ))      ; returns 230 because
                           ;   (list '+ a b) => '(+ 10 220)
(eval (list '+ 'a b))      ; returns 230 because
                           ;   (list '+ 'a b) => '(+ A 220)
                           ;   and A has the value 10
See the
eval
function in the