This really really should have moved to haskell-cafe as previously suggested (sending to both with this in mind); apologies for being a little confising to haskell-cafe This isn't a language design issue, it is a FAQ, or at best a nebulous conceptual debate (speaking of which, has anyone got something more specific than http://www.haskell.org/hawiki/ThatAnnoyingIoType). This question comes up again and again with Haskell newbies - the answer is of course you can't - not maybe, not sometimes, not sort of, but no. What you can do is confine the IO-ness at the outermost layer of the program - by seeding a psudo-random list at program initialization, as both solutions suggested - giving the original question the benefit of the doubt, we'll assume this was what the questioner wanted. Suggesting parameters is not an escape - it is exactly the same as using /dev/random in that they are also IO, weaker IO but still IO (getArgs:: IO [String], though there are counter arguments); besides, reproducability was not a requirement mentioned or implied by the original question (though relevent, not actually haskell specific.. haskell-cafe, again). Chaotic is not the same as Random (Jerzy you obviously know this, but please be clear about it, don't add to the confusion). Chaotic algoritms are used as a 'random-extender'. Random only happens when you seed you algorithm with a non-deterministic value (ie random). karczma wrote:
noise). I generated random fractals, etc. It didn't cost me anything to put different initializations by hand on every run when I wanted to have different behaviour. But it was MUCH more important to repeat the same sequence, e.g., after making fast some nice fractal sketch, I relaunched the program with bigger size/precision, but exploiting the same random sequence. I repeat, such is my philosophy. Yours is easier, since you are just discussing, most probably you never used RN for a serious work. If I am wrong, I apologize.
Jerzy K.
I have to say this.. SERIOUS WORK?! I don't know what Thomas does, but I'm working with security at the moment, and a "serious" random program with default constant seeding strikes me as serious and not in a good way. Overridable seeding sure, if the application demands it, but not broken by default. It's not random; it may be alright for screensavers, but it's not a good coding habit. Clive (Sorry, pet peeve)