'split' has type
split :: StdGen -> (StdGen, StdGen)
It takes a generator and produces two independent generators. The old
version of variant calls 'split' n times to get a new generator, and
it only calls "split" on the second result. The new version calls
split (log n) times. It gets a unique generator for each value of n
by using both results from split.
For example,
rands 2 r0 = let (r1, r2) = split r0
(r3, r4) = split r1
in r4
rands 3 r0 = let (r1,r2) = split r0
(r3',r4') = split r2
in r4'
Patrick
On Aug 14, 2008, at 4:57 AM, Johan Tibell wrote:
On Thu, Aug 14, 2008 at 12:15 PM, Patrick Perry
<[EMAIL PROTECTED]> wrote:
Actually, a much better solution is:
variant :: Int -> Gen a -> Gen a
variant v (Gen m) = Gen (\n r -> m n (rands r v))
where
rands r0 0 = r0
rands r0 n = let (r1,r2) = split r0
(n',s) = n `quotRem` 2
in case s of
0 -> rands r1 n'
_ -> rands r2 n'
It's not really clear to me how this works. Could you please explain?
Cheers,
Johan
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