Hi, Am 05.03.2009 um 10:13 schrieb bOR_:
Is there a reason why delay needs a force to be calculated?
delay creates a Delay object (Promise in Scheme). This can be passed around like eg. a Vector. When you want to retrieve the value, you have to use force, like get for a map. The first time the original value gets evaluated and the result gets cached. Subsequent calls to force then simply returns this cached result. I use Delays in my lazy-map package to provide a map, which evaluates the value of the keys lazily only when the user really accesses them. This is transparent to the code. (def x (lazy-hash-map :a (some-calculation) :b (other-calculation))) (x :a) ; <- no some-calculation happens(dissoc x :b) ; <- other-calculation never happens, because not accessed
However to provide such transparent usage, needed some plumbing around the Delays. Sincerely Meikel
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