CLHS: Macro NTH-VALUE

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Macro NTH-VALUE

Syntax:

nth-value n form => object

Arguments and Values:

n---a non-negative integer; evaluated.

form---a form; evaluated as described below.

object---an object.

Description:

Evaluates n and then form, returning as its only value the nth value yielded by form, or nil if n is greater than or equal to the number of values returned by form. (The first returned value is numbered `0`.)

Examples:

     (nth-value 0 (values 'a 'b)) =>  A
     (nth-value 1 (values 'a 'b)) =>  B
     (nth-value 2 (values 'a 'b)) =>  NIL
     (let* ((x 83927472397238947423879243432432432)
            (y 32423489732)
            (a (nth-value 1 (floor x y)))
            (b (mod x y)))
       (values a b (= a b)))
    =>  3332987528, 3332987528, true

Side Effects: None.

Affected By: None.

Exceptional Situations: None.

See Also:

multiple-value-list, nth

Notes:

Operationally, the following relationship is true, although nth-value might be more efficient in some implementations because, for example, some consing might be avoided.

     (nth-value n form) ==  (nth n (multiple-value-list form))

The following X3J13 cleanup issue, not part of the specification, applies to this section:

- NTH-VALUE:ADD

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