[Haskell-cafe] (...) Random generators

[Bardur Arantsson]

On 12/30/2011 04:38 PM, Jerzy Karczmarczuk wrote:
 > Bardur Arantsson:
 >> 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.
 >
 > Sure.
 > But the discussion on randomness is /per se/ interesting, especially in
 > a functional setting.
 >
 > Anyway, nobody can convince Steve Horne. Perhaps as an "unintentional"
 > side-effect...
 >
 > But random streams, or rather pseudo-random streals (infinite lazy
 > lists, as the example I gave, the `iterate` of `next`) are as
 > referentially transparent as any Haskell data. Really.
 >

Of course -- if you just have a starting seed and the rest of the 
sequence is known from there. I was thinking of e.g. those "periodic 
re-initialization" ways of doing RNG.

 > I *NEVER* used
 > "true" random numbers, even to initialize a generator, since in the
 > simulation business it is essential that you can repeat the sequence on
 > some other platform, with some other parameters, etc.
 >

I've heard this a lot from physicists -- of course if you run a 
simulation reproducibility can be extremely important (e.g. for 
double-checking computations across different machines). However, if 
you're doing crypto it may not be so desirable :).

Anyway, I'm out of this thread too :).

Cheers,