(r5rs.info.gz) Delayed evaluation
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4.2.5 Delayed evaluation
------------------------
-- library 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 Control features)
for a more complete description of `delay'.
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