| place | place with numeric value |
| increment | numeric value |
INCF macro modifies a place with numeric value. Its value is incremented by increment number. Default increment is 1.
(let ((a 10)) (incf a) a) => 11 (let ((a 10)) (incf a 2.3) a) => 12.3 (let ((a 10)) (incf a -2.3) a) => 7.7 (let ((a (list 10 11 12 13))) (incf (elt a 2) 2.3) a) => (10 11 14.3 13)