make a random text token, using MonadRandom and friends

randomstr5.hs

module RandomStr5 where

-- uses `MonadRandom` package

import           Control.DeepSeq      (force)
import           Control.Monad        (liftM)
import           Control.Monad.Random (evalRandIO, getRandoms)
import           Data.List            (nub)
import           Data.Text            (Text, pack)

------------------------------------------------------------------------

-- TODO: Hard-coding length here (as opposed to passing length as a
-- parameter) seems to make this go ~10x faster, at least in ghci.
-- But why?
randomStr :: IO Text
randomStr = pack <$> liftM (map toChar) (makeStr 12)
    where
        makeStr :: Int -> IO String
        makeStr len = evalRandIO $ liftM (take len) getRandoms

        toChar :: Enum a => a -> Char
        toChar i = chars !! (fromEnum i `mod` length chars)

        chars :: String
        chars = ['0'..'9'] ++ ['A'..'Z'] ++ ['a'..'z']

allUnique :: IO Bool
allUnique = do
    xs <- mapM (const randomStr) [1..1000]
    return (force(xs) == force(nub xs))

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

------------------------------------------------------------------------