• Source 
    1. import System.Random
    2. import Data.List
    3.  
    4. randomDbls :: StdGen -> [ Double ]
    5. randomDbls= randomRs (0,1)
    6.  
    7. chooseItem is ws r = let 
    8.     folder a b = a : map ( + a ) b
    9.     selecter  r ( i, ( f, t ) ) = f <= r && r < t
    10.     ts = foldr folder [ ] ws 
    11.     fs = 0 : ts
    12.     ifts = zip is $ zip fs ts
    13.     in fst $ head $ filter ( selecter r ) ifts 
    14.  
    15. main = do
    16.     rds <- ( return . randomDbls ) =<< getStdGen 
    17.     print $ map (chooseItem ['A'..'C' ] [0.4,0.5,0.1] ) $ take 100 rds