ToC DocOverview CGDoc RelNotes Index PermutedIndex
Allegro CL
Home Previous Up Next Table of Contents Index
  ANSI Common Lisp   5 Data and Control Flow   5.3 Dictionary of Data and Control Flow

5.3.53 values Accessor

values &rest object    {object}*

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

Arguments and Values:
object - an object.

place - a place.

new-value - an object.

values returns the objects as multiple values2.

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

 (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

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:

Home Previous Up Next Table of Contents Index
© Franz Inc. All Rights Reserved - File last updated 2022-07-25