Unsafe functions

There are a number of unsafe functions in the libraries.

• unsafePerformIO :: IO a -> a
• unsafeInterleaveIO :: IO a -> IO a
• unsafeInterleaveST :: ST s a -> ST s a
• unsafeIOToST :: IO a -> ST s a
• unsafeIOToSTM :: IO a -> STM a
• unsafeFreeze, unsafeThaw
• unsafeCoerce# :: a -> b
• seq :: a -> b -> b

Unsafe functions can break type safety (unsafeCoerce#, unsafePerformIO), interfere with lazy IO (unsafeInterleaveIO), or break parametricity (seq). Their use (except in the case of seq) would require some kind of assurance on the part of the programmer that what they're doing is safe.

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