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The IO monad
The IO monad allows controlled introduction of
other effect-ful language features (not just I/O)
State
newRef :: IO (IORef a)
read :: IORef s a -> IO a
write :: IORef s a -> a -> IO ()
Concurrency
fork :: IO a -> IO ThreadId
newMVar :: IO (MVar a)
takeMVar :: MVar a -> IO a
putMVar :: MVar a -> a -> IO ()