Seed.hs

module Test.Framework.Seed where

import Test.Framework.Utilities

import System.Random (StdGen, mkStdGen, randomIO)

import Data.Char ( toLower )


data Seed = FixedSeed Int
          | RandomSeed

instance Show Seed where
    show RandomSeed    = "random"
    show (FixedSeed n) = show n

instance Read Seed where
    readsPrec prec xs = if map toLower random_prefix == "random"
                        then [(RandomSeed, rest)]
                        else map (FixedSeed `onLeft`) (readsPrec prec xs)
      where (random_prefix, rest) = splitAt 6 xs

-- | Given a 'Seed', returns a new random number generator based on that seed and the
-- actual numeric seed that was used to build that generator, so it can be recreated.
newSeededStdGen :: Seed -> IO (StdGen, Int)
newSeededStdGen (FixedSeed seed) = return $ (mkStdGen seed, seed)
newSeededStdGen RandomSeed = newStdGenWithKnownSeed

newStdGenWithKnownSeed :: IO (StdGen, Int)
newStdGenWithKnownSeed = do
    seed <- randomIO
    return (mkStdGen seed, seed)