delay -- r7rs Definition

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Kind

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syntax;

Implemented by

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• delay (from vonuvoli);

Syntax signature

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Syntax keywords:

• expression: expression;

Syntax variants:

• (_ expression)

Exports

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• scheme:lazy -- (scheme lazy);

Exports recursive

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• scheme -- (scheme);

Description

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(delay <expression>)

Semantics: The delay construct is used together with the procedure force to implement lazy evaluation or call by need. (delay <expression>) returns an object called a promise which at some point in the future can be asked (by the force procedure) to evaluate <expression>, and deliver the resulting value. The effect of <expression> returning multiple values is unspecified.

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The text herein was sourced and adapted as described in the "R7RS attribution of various text snippets" appendix.