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This puzzle seems far too simple for the use of data structures or even monads. A single tail recursive helper function does the trick.

```-- Linear solution by Chris Kuklewicz <haskell@list.mightyreason.com>

-- It is important to realize you are picking from the possible
-- combinations of the digits from 0 to (n-1).  The probability that
-- an element is chosen is (r/n).  This "rolls the dice" for each element
-- of the range in ascending order.
module Main where

import System.Random
import System(getArgs)

main = do [r,n] <- fmap (map read) getArgs
g <- newStdGen
mapM_ print (pick r n g)

pick :: Int -> Int -> StdGen -> [Int]
pick r n g  | 0<=r && r<=n  = pick' r n g 0
| otherwise  = fail "r must be between 0 and n"
where pick' 0 _ _  _ = []
pick' r n g1 i | r==n = [i..(i+n-1)]
| otherwise =
let (x,g2) = randomR (1,n) g1
in if x <= r
then i : (pick' (pred r) (pred n) g2 \$! (succ i))
else      pick' r        (pred n) g2 \$! (succ i)
```