| place | place with numeric value |
| decrement | numeric value |
DECF macro modifies a place with numeric value. Its value is decremented by decrement number. Default decrement is 1.
(let ((a 10)) (decf a) a) => 9 (let ((a 10)) (decf a 2.3) a) => 7.7 (let ((a 10)) (decf a -2.3) a) => 12.3 (let ((a (list 10 11 12 13))) (decf (elt a 2) 2.3) a) => (10 11 9.7 13)