Hi, as far as I know, a random generator usually creates an int or a sequence of bits, right? Or do you have some specific random generators in mind? I personally do not think it is worth to modify the Random module, which dates back to at least Haskell 98. Maybe a new package on the Hackage? Cheers, Milan
Hello, RandomGen and Random classes assume generators produce Int values. This is non-ideal as many high speed generators produce special values (ex: doubles) or generic values (bit streams / bytestrings) that can be converted directly to types easier than coercing to Int then to an 'a' via the Random class.
See 4315 [1] for the patch.
Period of discussion: Till October 8 (3.5 weeks, giving a little time after ICFP for last minute debate)
Specifically, this proposal:
1) Alters RandomGen:
from: class RandomGen g where next :: g -> (Int, g) genRange :: g -> (Int, Int)
to
class RandomGen g v | g -> v where next :: g -> (v, g) genRange :: g-> (v,v)
2) Alters Random:
From:
class Random a where randomR :: RandomGen g => (a,a) -> g -> (a,g) random :: RandomGen g => g -> (a, g) randomRs :: RandomGen g => (a,a) -> g -> [a] randoms :: RandomGen g => g -> [a] randomRIO :: (a,a) -> IO a randomIO :: IO a
to
class Random a where randomR :: RandomGen g v => (a,a) -> g -> (a,g) random :: RandomGen g v => g -> (a, g) randomRs :: RandomGen g v => (a,a) -> g -> [a] randoms :: RandomGen g v => g -> [a]
Additional Points of Debate 1) Because random[R]IO can not be part of the new Random instance with a sensible default, these have been moved to top-level functions:
randomRIO :: (Random a Int) => (a,a) -> IO a randomIO :: (Random a Int) => IO a
Other options exist and I'm open to them. I'm just being upfront about what the patch currently does.
2) All pre-existing instances of "Random x" for some concrete 'x' have been modified to be "instance Random x Int". As 'Int' was the previous (hardcoded) default for RandomGen this is simply matching the behavior. More instances are possible and probably make sense now. Alternatively, one could argue for zero default instance as they can collide with how a particular user wishes types to be coerced.
3) Not-so-new extensions are used to enable these changes. Extensions include MultiParamTypeClasses, FlexibleContexts, and FunDeps.
4) A patch is included bumping the version from 1.0.0.x to 1.1.0.0.
Cheers, Thomas
[1] http://hackage.haskell.org/trac/ghc/ticket/4315 _______________________________________________ Libraries mailing list Libraries@haskell.org http://www.haskell.org/mailman/listinfo/libraries