delay

produces a delayed evaluation

Returns a promise that, when forced, evaluates the expressions, returning the final evaluated result. The result is then cached, so further uses of force return the cached value immediately.

An Example

(define p (delay
            (println "hello once")
            "hello"))
(force p) ;; prints "hello once"
(force p)

The first invocation of p will print “hello once” to the console, and also return the string “hello”. Subsequent invocations of p will only return “hello”.