Re: [Haskell-cafe] [ANN] random-stream package

Manlio Perillo writes:

Gökhan San ha scritto:

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Manlio Perillo writes:

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The stream generator implements tha RandomGen interface.

This is really cool, though I think 'split' is a must. Maybe all instances could share the same stream in the background, then it wouldn't cause resource issues.

I have thought about this, but is it safe? I feared that this would break referential transparency.

You're absolutely right, my bad. To test locally, I wrote a split function by merging Stream with StdGen, but I'm not sure if it makes much sense statistically:

data Stream = Stream StdGen L.ByteString

instance RandomGen Stream where next (Stream t s) = (xor it (fromIntegral is), Stream t' s') where (it, t') = next t (is, s', _) = (runGetState getWordhost) s 0 split (Stream t s) = let (left, right) = split t in (Stream left s, Stream right s)

I'd love to test how it scales if you happen to implement split on the stream.

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Also, IMHO mkStream should produce an IO Stream (like getStdGen), as current implementation isn't referentially transparent; let the library user decide whether to use unsafePerformIO.

The basic idea is that there is this system wide random number generator, that is always available. That's the reason why mkIOStream is hidden.

Ah, OK, I get it now. -- Gökhan San