[Haskell-beginners] theStdGen unsafePerformIO

[John Smith]

Why does theStdGen require unsafePerformIO? I recompiled the Random module with

theStdGen :: IO (IORef StdGen)
theStdGen  = do
                 rng <- mkStdRNG 0
                 newIORef rng

The implementations of a few functions needed to change slightly (to extract the IORef from IO), but no other type 
signatures needed changing, and nothing blew up.