place—a place.
delta-form—a form; evaluated to produce a delta.
The default is 1
.
delta—a number.
new-value—a number.
incf
and decf
are used for incrementing and
decrementing the value of place, respectively.
The delta is
added to (in the case of incf
)
or subtracted from (in the case of decf
)
the number in place and the result is stored in place.
Any necessary type conversions are performed automatically.
For information about the evaluation of subforms of places, see Section 5.1.1.1 (Evaluation of Subforms to Places).
(setq n 0) (incf n) → 1 n → 1 (decf n 3) → -2 n → -2 (decf n -5) → 3 (decf n) → 2 (incf n 0.5) → 2.5 (decf n) → 1.5 n → 1.5
Place is modified.