randomstr3.hs

module RandomStr3 where

-- uses mwc-random for making random strings

import           Data.List           (nub)
import           Data.Text           as T (Text, pack)
import qualified Data.Vector.Unboxed as V (Vector, map, toList)
import           Data.Word           (Word8)
import           System.Random.MWC   (asGenST, uniformVector, withSystemRandom)

randomStr :: Int -> IO Text
randomStr len = do
    v <- withSystemRandom . asGenST $ \gen -> uniformVector gen len
    return $ T.pack $ V.toList $ V.map toChar (v :: V.Vector Word8)

toChar :: Enum a => a -> Char
toChar i = chars !! (c `mod` len)
    where
        c     = fromEnum i
        chars = ['0'..'9'] ++ ['A'..'Z'] ++ ['a'..'z']
        len   = length chars

allUnique :: IO Bool
allUnique = do
    xs <- mapM (\_ -> randomStr 12) [1..1000]
    return $ xs == nub xs

main :: IO ()
main = allUnique >>= print