[Haskell-cafe] random question

[Luke Palmer]

On Wed, Oct 7, 2009 at 2:59 PM, Michael Mossey <mpm at alumni.caltech.edu> wrote:
> My thread about randomness got hijacked so I need to restate my remaining
> question here. Is it acceptable to write pure routines that use but do not
> return generators, and then call several of them from an IO monad with a
> generator obtained by several calls to newStdGen?

It's gross.  What if you don't want IO as part of this computation?

If you have a random generator that supports splitting (something
rather hard to do from what I understand), I prefer not to return the
new generator but instead to split it.  So, using your shuffle:

> shuffle :: RandomGen g => g -> [a] -> [a]
> shuffle = ...

foo :: RandomGen g => [a] -> [a] -> g -> ([a],[a])
foo xs ys gen =
  let (gen1, gen2) = split gen in
  (shuffle gen1 xs, shuffle gen2 ys)

Luke