Proposal: Move 'split' into a separate class in System.Random

[Simon Peyton-Jones]

| > (Oh now I see Ivan mentions existing PRNGs that don't (can't?) support
| > split... that may be a reasonable argument; I'll have to think about it; is
| > this the main motivation? or just one observation among many?)
| 	
| I think it's the main one; that things like the Mersenne twister can't be
| made instances of Random has stuck in people's craws for a while.

In GHC's unique-supply generator we use a trick due to Lennart Augustsson to turn a linear generator (such as the Mersenne twister) into a splittable one.

Code is here: http://darcs.haskell.org/ghc/compiler/basicTypes/UniqSupply.lhs

Maybe the same would work for Mersenne. 

(Yes it uses unsafeInterleaveIO under the hood.)

Simon

| -----Original Message-----
| From: libraries-bounces at haskell.org [mailto:libraries-bounces at haskell.org] On
| Behalf Of Brandon S Allbery KF8NH
| Sent: 15 September 2010 05:01
| To: libraries at haskell.org
| Subject: Re: Proposal: Move 'split' into a separate class in System.Random
| 
| -----BEGIN PGP SIGNED MESSAGE-----
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| 
| On 9/14/10 23:44 , Isaac Dupree wrote:
| > (Oh now I see Ivan mentions existing PRNGs that don't (can't?) support
| > split... that may be a reasonable argument; I'll have to think about it; is
| > this the main motivation? or just one observation among many?)
| 	
| I think it's the main one; that things like the Mersenne twister can't be
| made instances of Random has stuck in people's craws for a while.
| 
| - --
| brandon s. allbery     [linux,solaris,freebsd,perl]      allbery at kf8nh.com
| system administrator  [openafs,heimdal,too many hats]  allbery at ece.cmu.edu
| electrical and computer engineering, carnegie mellon university      KF8NH
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