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cl:macros:nth-value [2019/08/16 12:00] |
cl:macros:nth-value [2019/08/23 05:00] (current) |
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| + | ====== Macro NTH-VALUE ====== | ||
| + | |||
| + | ====Syntax==== | ||
| + | * **nth-value** //n form// → //object// | ||
| + | |||
| + | ====Arguments and Values==== | ||
| + | * //n// - a non-negative //[[CL:Glossary:integer]]//; evaluated. | ||
| + | * //form// - a //[[CL:Glossary:form]]//; evaluated as described below. | ||
| + | * //object// - an //[[CL:Glossary:object]]//. | ||
| + | |||
| + | ====Description==== | ||
| + | Evaluates //n// and then //form//, returning as its only value the //n//th value //[[CL:Glossary:yield|yielded]]// by //form//, or **[[CL:Constant Variables:nil]]** if //n// is greater than or equal to the number of //[[CL:Glossary:value|values]]// returned by //form//. (The first returned value is numbered ''0''.) | ||
| + | |||
| + | ====Examples==== | ||
| + | <blockquote> | ||
| + | (nth-value 0 ([[CL:Functions:values]] 'a 'b)) <r>A</r> | ||
| + | (nth-value 1 ([[CL:Functions:values]] 'a 'b)) <r>B</r> | ||
| + | (nth-value 2 ([[CL:Functions:values]] 'a 'b)) <r>[[CL:Constant Variables:NIL]]</r> | ||
| + | ([[CL:Special Operators:let-star|let*]] ((x 83927472397238947423879243432432432) | ||
| + | (y 32423489732) | ||
| + | (a (nth-value 1 ([[CL:Functions:floor]] x y))) | ||
| + | (b ([[CL:Functions:mod]] x y))) | ||
| + | ([[CL:Functions:values]] a b ([[CL:Functions:math-equal|=]] a b))) <r>3332987528 | ||
| + | 3332987528 | ||
| + | //[[CL:Glossary:true]]//</r> | ||
| + | </blockquote> | ||
| + | |||
| + | ====Side Effects==== | ||
| + | None. | ||
| + | |||
| + | ====Affected By==== | ||
| + | None. | ||
| + | |||
| + | ====Exceptional Situations==== | ||
| + | None. | ||
| + | |||
| + | ====See Also==== | ||
| + | * **[[CL:Macros:multiple-value-list|Macro MULTIPLE-VALUE-LIST]]** | ||
| + | * **[[CL:Functions:nth|Function NTH]]** | ||
| + | |||
| + | ====Notes==== | ||
| + | Operationally, the following relationship is true, although **[[CL:Special Operators:nth-value]]** might be more efficient in some //[[CL:Glossary:implementation|implementations]]// because, for example, some //[[CL:Glossary:consing]]// might be avoided. | ||
| + | |||
| + | <blockquote> | ||
| + | (nth-value //n// //form//) ≡ ([[CL:Functions:nth]] //n// ([[CL:Macros:multiple-value-list]] //form//)) | ||
| + | </blockquote> | ||
| + | |||
| + | \issue{NTH-VALUE:ADD} | ||
