[Haskell-cafe] On the purity of Haskell /Random generators

[Bardur Arantsson]

On 12/29/2011 09:39 PM, Jerzy Karczmarczuk wrote:
>
> "Truly random" numbers are very rarely used, forget about them.

Well, obviously, but why should we forget about them? The usual 
approach(*) is to gather entropy from a truly(**) random source
and use that to seed (and perhaps periodically re-seed) a PRNG.

(*) At least as far as I understand it.
(**) At least one believed to be truly random.

My point was simply to make clear the distinction between RNG vs. PRNG.

> "Standard" r. generators (pseudo-random) in Haskell are monadic, because
> the relevant algorithms are stateful.
> Congruential, Fibonacci, Mersenne Twister, whatever, is a function, more
> or less:
> (newValue,newSeed) = rgen seed
>
> The monadic approach serves mainly to hide the seed.
> Some people prefer to use random streams, no monads, so the question of
> Steve Horne is not universal.

Random streams are not referentially transparent, though, AFAICT...?

Either way this thread has gone on long enough, let's not prolong it 
needlessly with this side discussion.