Ryan Newton
There implementation has two major pieces: (1) Sources of random bits (class RandomGen) (2) Instances of class Random that map use random bits to create Haskell types
I'd say there are three pieces, initial entropy (clock, external seed, system crypto random generator), deterministic generator interface (PRNG, the RandomGen class), and the instances of that class. I tried to answer the first item in System.Crypto.Random. The 'random' package never really had an answer for entropy and I'm not sure what the community thinks about that. Perhaps answering this problem in slightly obscure packages is OK.
The issue is that the legacy RandomGen API isn't very good at generating random bits.
Agreed. This is why CryptoRandomGen uses ByteString (so we can generate any number of BYTES of random values). As I tried to argue when I make RandomGen more polymorphic, this is an issue with hardcoding the type as Int. Unfortunately, people didn't accept that alteration and I feel continuing to generating Int while allowing devs to discover the amount of entropy isn't taking things far enough.
I'd also be happy to hear other proposals for API changes and additions.
As I say below, I don't understand why we can't use ByteString. There are (or should be) rather fast decodings of all the popular primitive types from bytestrings, so this takes care of our polymorphism issue. I accept that, unlike the CryptoRandomGen, we don't want an explicit failure for RandomGen. But how about a common interface for instantiating generators ('newGen')? Is there a reason not to have that? --- CODE --- class RandomGen g where next :: g -> (Int, g) nextBits :: g -> BitLength -> (ByteString, g) genBits :: g -> Int newGen :: ByteString -> g --- END CODE --- Also, perhaps we could still have an explicit reseed? --- CODE --- class Reseedable g where reseed :: g -> Bytestring -> g --- END CODE --- I'll stop here before I entirely recreate CryptoRandomGen, but without the explicit errors and in more classes (the next step would be a method for querying how much entropy is needed for instantiation).
System.Random can't depend on bytestring, so I doubt we want block RNG in the RandomGen class.
Why can't it? System.Ranomd isn't part of H2010 and H98 already needs its own random module. I'll try to make time to review the code, you'll hear if I do. Cheers, Thomas