# Difference between revisions of "Talk:99 questions/Solutions/23"

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The more elegant solution using randomRs does not save the new random state and is thus dangerous to use if randomness is important.

## some notes

the signature of removeAt is:

```   removeAt :: Int -> [a] -> (a, [a])
```

so we have to exchange the orders of parameters in the calls of remove at from:

```   removeAt l (k+1)
```

to:

```   removeAt (k+1) l
```

and we have to extract the remaining list from the result as well:

```   snd \$ removeAt (k+1) l
```

so the full version should be:

```   rnd_select2 :: RandomGen g => [a] -> Int -> g -> ([a], g)
rnd_select2 _ 0 gen = ([], gen)
rnd_select2 [] _ gen = ([], gen)
rnd_select2 l count gen
| count == (length l) = (l, gen)
| otherwise           =  rnd_select2 (snd \$ removeAt (k+1) l) count gen'
where (k, gen') =
randomR (0, (length l) - 1) gen
```
```   rnd_selectIO :: [a] -> Int -> IO [a]
rnd_selectIO l count = getStdRandom \$ rnd_select2 l count
```