Revised(5) Report on the Algorithmic Language Scheme - Delayed evaluation

### 4.2.5 Delayed evaluation

    Syntax:  (delay <expression>)

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 may be asked (by the force procedure) to evaluate <expression>, and deliver the resulting value. The effect of <expression> returning multiple values is unspecified.

See the description of force (section 6.4) for a more complete description of delay.