[Haskell-cafe] Generate random UArray in constant memory space.

9 Feb 2010

      Hello Cafe,

I tried to generate memory-efficient list of random numbers, so I've
used uvector library for this task. But it doesn't work,
it still allocates more than 6Gb of memory for the random list of 10
million elements. Here is the code:
...
import Text.Printf
import System.Random
import Control.Applicative
import System.Environment
import Data.Array.Vector
...
randomListU :: (Int, Int) -> StdGen -> Int -> (UArr Int)
randomListU b g size = unfoldU size gen g
  where gen g = let (x, g') = randomR b g
                in JustS (x :*: g')
...
main = do
  [size] <- map read <$> getArgs
  let ints = randomListU (-10, 10) (mkStdGen 1) size
  printf "%d\n"  (sumU ints)
Could someone give a hint, how to implement this function in constant
memory space?

Thank you in advance.

Best regards,
Vasyl Pasternak