Unsafe functions

[Using the FFI] you can import any C function with a pure type, which also allows you to wreak arbitrary havoc. We enable the user to disguise arbitrary machine code as a Haskell function of essentially arbitrary type. In comparison, unsafePerformIO seems angelic.

Manuel Chakravarty

There are a number of unsafe functions in the libraries.

• unsafeLocalState :: IO a -> a
• unsafePerformIO :: IO a -> a
• inlinePerformIO :: 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

Unsafe functions can:

• break type safety (unsafeCoerce#, unsafeLocalState, unsafePerformIO),

• or break equational reasoning (unsafeInterleaveIO).

Their use would require some kind of assurance on the part of the programmer that what they're doing is safe.

unsafe is also a keyword which can be used in a foreign import declaration.

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