The (scheme lazy) library exports procedures and syntax keywords for lazy evaluation.

For more information see the R⁷RS Scheme Specification.

• delay
• force
• delay-force
• make-promise
• promise?

delay

(delay {expression})

Return a promise object that can be asked in the future (via force) to evaluate {expression} and return the result.

force

(force promise)

Force the value of a promise.

delay-force

(delay-force {expression})

make-promise

(make-promise obj)

Return a promise which will return obj when forced. This function is similar to delay but does not delay its argument: it is a procedure rather than syntax. If obj is already a promise, it is returned.

promise

(promise? obj)

Returns #t if object is a promise, and #f otherwise.