This topic should be posed to a more general forum than GHusers... Jens Fisseler answers:
Is it possible to generate random numbers that are "unique" in O(1) in Haskell?
Of course, I could create unique numbers by incrementing a global value, but for security reasons I need random numbers.
do you really need random numbers? If not: I vaguely remember an algorithm from one of the "Graphic Gems" books, implementing some sort of fancy counter which goes through all numbers from 0,...,2^n-1 in a seemingly random, but of course deterministic and repeatable order.
Actually, decent random number generators, even simple congruential ones: X_{n+1} = A*X_n + C (mod M) if the parameters are chosen correctly, *guarantee* to generate ALL M integers between 0 and M-1 without repetitions, and only then the sequence repeats. Take M sufficiently large, and you are safe, provided you know what you are doing. See Knuth for details, how to choose the params. Another story -- of course -- is the generation of RN in Haskell. Too often, too many people suggest all these horrible manadic devices, while the usage of a simple lazy stream of consecutively generated numbers would suffice... Bon courage. Jerzy Karczmarczuk