randomstr1.hs

-- copied from Network.Mail.Mime

module RandomStr where

import           Control.Arrow (first)
import           Data.List     (nub)
import           System.Random

randomString :: RandomGen d => Int -> d -> (String, d)
randomString len =
    first (map toChar) . sequence' (replicate len (randomR (0, 61)))
    where
        sequence' [] g = ([], g)
        sequence' (f:fs) g =
            let (f', g') = f g
                (fs', g'') = sequence' fs g'
            in (f' : fs', g'')

        toChar i
            | i < 26 = toEnum $ i + fromEnum 'A'
            | i < 52 = toEnum $ i + fromEnum 'a' - 26
            | otherwise = toEnum $ i + fromEnum '0' - 52

randomStr :: Int -> IO String
randomStr n = do
    g <- newStdGen
    let (s, _) = randomString n g
    return s

allUnique :: IO Bool
allUnique = do
    xs <- mapM (\_ -> randomStr 12) [1..10000]
    return $ xs == nub xs

main :: IO ()
main = allUnique >>= putStrLn . show