Movatterモバイル変換

Syntax:

prog1first-formform* =>result-1

prog2first-form second-formform* =>result-2

Arguments and Values:

first-form---aform; evaluated as described below.

second-form---aform; evaluated as described below.

forms---animplicit progn; evaluated as described below.

result-1---theprimary value resulting from theevaluation offirst-form.

result-2---theprimary value resulting from theevaluation ofsecond-form.

Description:

prog1evaluatesfirst-form and thenforms,yielding as its onlyvalue theprimary valueyielded byfirst-form.

prog2evaluatesfirst-form, thensecond-form, and thenforms,yielding as its onlyvalue theprimary valueyielded byfirst-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:

multiple-value-prog1,progn

Notes:

prog1 andprog2 are typically used toevaluate one or moreforms with side effects and return avalue 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*))