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gcd Numbers Dictionary lcm
Macro

incf, decf

incf place [delta-form] ⇒ new-value

decf place [delta-form] ⇒ new-value

Arguments and Values

placea place.
delta-forma form; evaluated to produce a delta. The default is 1.
deltaa number.
new-valuea number.

Description

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 Evaluation of Subforms to Places.

Examples

 (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

Side Effects

Place is modified.

See Also

+, -, 1+, 1-, setf; psetf

Backlinks

1+, 1-, Evaluation of Subforms to Places, getf, Numbers Dictionary, Numeric Operations, Overview of Places and Generalized Reference, Symbols in the COMMON-LISP Package, Treatment of Other Macros Based on SETF, unwind-protect