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

19 Mar 2009

      Hi.

I'm pleased to announce the availability of my random-stream package.
The cabalized package is available at:
http://haskell.mperillo.ath.cx/random-stream-0.0.1.tar.gz

Note that I have not uploaded it on Hackage, and I do not plan to upload 
it in the near future, at least until I will repute the package mature 
enough.

 From package description:
     Portable interface for the operating system source of pseudo
     random data.

     Supported sources are Unix /dev/urandom, Win32 CryptGenRandom and
     OpenSSL pseudo random numbers generator.

     This package is based on idea from os.urandom implementation, in
     CPython.

The idea is to view the system pseudo random generator as a stream of 
infinite random bytes.

So, I have used a lazy bytestring, and
unsafePerformIO/unsafeInterleaveIO.

The underlying data is:
newtype Stream = Stream L.ByteString

and the constructor *is exposed*.

The package configuration *must* be done using a flag to specify the 
"source" to use.

As an example:

runghc Setup.hs configure -O2 -fHAVE_URANDOM
runghc Setup.hs configure -O2 -fHAVE_SSL
runghc Setup.hs configure -O2 -fHAVE_WIN32_CRYPT

If the flag is not specified, the compilation will fail.
Note that Windows it not yet supported.

The stream generator implements tha RandomGen interface.

Some notes:
1) The system *pseudo* random generator is used.
    As an example, on Linux, /dev/random produces "true" random numbers,
    but it may block if there is not enough entropy in the system.
    More details on
    http://en.wikipedia.org/wiki//dev/random
2) When reading data, the lazy bytestring chunk size is used.
    The default chunk size, however, is fine when reading from a regular
    file, but may not be the best choice when reading pseudo random
    numbers.

    For SSL (and Windows) support, the chunk size can be easily changed;
    but for Unix support this seems to not be possible, unless I
    reimplement hGetContents.

    The Data.ByteString.Lazy module have an hGetContentsN function.
    Unfortunately it is not exposed.
    I find this annoying; is it possible to export the *N functions
    from Data.ByteString.Lazy.Internal?
3) I have tested the package on Debian Linux Etch, using GHC 6.8.2.

Feedback will be appreciate.
I not sure about some details.

Usage example:

module Main where

import System.Random
import System.Random.Stream

gen = mkStream
l :: [Int]
l = randoms gen :: [Int]

main = do
   print l

Manlio Perillo