values

ToC

Allegro CL

ANSI Common Lisp

5 Data and Control Flow

5.3 Dictionary of Data and Control Flow

5.3.53 values

Accessor

Syntax:

values &rest object

{object}*

(setf (values &rest place) new-values)

Arguments and Values:

object - an object.

place - a place.

new-value - an object.

Description:

values returns the objects as multiple values₂.

setf of values is used to store the multiple values₂ new-values into the places. See Section 5.1.2.3 VALUES Forms as Places.

Examples:

 (values)   < no values > 
 (values 1)  1
 (values 1 2)  1, 2
 (values 1 2 3)  1, 2, 3
 (values (values 1 2 3) 4 5)  1, 4, 5
 (defun polar (x y)
   (values (sqrt (+ (* x x) (* y y))) (atan y x)))   POLAR
 (multiple-value-bind (r theta) (polar 3.0 4.0)
   (vector r theta))
 #(5.0 0.927295)

Sometimes it is desirable to indicate explicitly that a function returns exactly one value. For example, the function

 (defun foo (x y)
   (floor (+ x y) y))   FOO

returns two values because floor returns two values. It may be that the second value makes no sense, or that for efficiency reasons it is desired not to compute the second value. values is the standard idiom for indicating that only one value is to be returned:

 (defun foo (x y)
   (values (floor (+ x y) y)))   FOO

This works because values returns exactly one value for each of args; as for any function call, if any of args produces more than one value, all but the first are discarded.

See Also:

values-list, multiple-value-bind, multiple-values-limit, Section 3.1 Evaluation

Notes:

Since values is a function, not a macro or special form, it receives as arguments only the primary values of its argument forms.

Allegro CL Implementation Details:

None.