![[XANALYS]](../Graphics/XanSmall.gif)
Syntax:
prog1 first-form form* => result-1
prog2 first-form second-form form* => result-2
Arguments and Values:
first-form---a form; evaluated as described below.
second-form---a form; evaluated as described below.
forms---an implicit progn; evaluated as described below.
result-1---the primary value resulting from the evaluation of first-form.
result-2---the primary value resulting from the evaluation of second-form.
Description:
prog1 evaluates first-form and then forms, yielding as its only value the primary value yielded by first-form.
prog2 evaluates first-form, then second-form, and then forms, yielding as its only value the primary value yielded by first-form.
Examples:
(setq temp 1) => 1
(prog1 temp (print temp) (incf temp) (print temp))
>> 1
>> 2
=> 1
(prog1 temp (setq temp nil)) => 2
temp => NIL
(prog1 (values 1 2 3) 4) => 1
(setq temp (list 'a 'b 'c))
(prog1 (car temp) (setf (car temp) 'alpha)) => A
temp => (ALPHA B C)
(flet ((swap-symbol-values (x y)
(setf (symbol-value x)
(prog1 (symbol-value y)
(setf (symbol-value y) (symbol-value x))))))
(let ((*foo* 1) (*bar* 2))
(declare (special *foo* *bar*))
(swap-symbol-values '*foo* '*bar*)
(values *foo* *bar*)))
=> 2, 1
(setq temp 1) => 1
(prog2 (incf temp) (incf temp) (incf temp)) => 3
temp => 4
(prog2 1 (values 2 3 4) 5) => 2
Side Effects: None.
Affected By: None.
Exceptional Situations: None.
See Also:
Notes:
prog1 and prog2 are typically used to evaluate one or more forms with side effects and return a value that must be computed before some or all of the side effects happen.
(prog1 form*) == (values (multiple-value-prog1 form*)) (prog2 form1 form*) == (let () form1 (prog1 form*))