Yes, dropping 1000000000 entries is bad, 'someGenerator' was thought as an deputy only. In reality I have some sort of generator which generates a large system state varying over time. It was my fault I didn't state this clearly. Thank you for the interesting reading about RNGs anyway. Michael Am 07.11.2016 um 21:56 schrieb Edward Z. Yang:
It's not guaranteed. Unfortunately there aren't really good ways to avoid sharing; the general advice is to convert values into functions, and apply them at the use site where sharing is OK.
Unrelatedly, in your sample code, dropping 1000000000 entries is not a good way to build a splittable RNG. Check out http://publications.lib.chalmers.se/records/fulltext/183348/local_183348.pdf and also its related work for some bettera pproaches.
Edward
Excerpts from Michael Roth's message of 2016-11-07 20:56:54 +0100:
Hello! A short question, given:
data Seed = ... data Value = ...
someGenerator :: Seed -> [Value]
createTwo :: Seed -> ([Value], [Value]) createTwo s = (as, bs) where as = someGenerator s bs = drop 1000000000 (someGenerator s)
Is it guaranteed that 'someGenerator s' is created twice and not shared between 'as' and 'bs'? Is this by language design? Are there any GHC options that change the behaviour?
Thank you,
Michael