Difference between revisions of "Unsafe functions"
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* <hask>unsafeIOToST :: IO a -> ST s a</hask> |
* <hask>unsafeIOToST :: IO a -> ST s a</hask> |
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* <hask>unsafeIOToSTM :: IO a -> STM a</hask> |
* <hask>unsafeIOToSTM :: IO a -> STM a</hask> |
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− | * <hask>unsafeFreeze, unsafeThaw</hask> |
+ | * <hask>unsafeFreeze</hask>, <hask>unsafeThaw</hask> |
* <hask>unsafeCoerce# :: a -> b</hask> |
* <hask>unsafeCoerce# :: a -> b</hask> |
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* <hask>seq :: a -> b -> b</hask> |
* <hask>seq :: a -> b -> b</hask> |
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− | Unsafe functions can break |
+ | Unsafe functions can break: |
+ | |||
⚫ | |||
+ | * type safety (<code>unsafeCoerce#</code>, <code>unsafePerformIO</code>), |
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+ | |||
+ | * [https://okmij.org/ftp/Haskell/index.html#lazyIO-not-True breaks equational reasoning] (<code>unsafeInterleaveIO</code>), |
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+ | |||
⚫ | |||
+ | |||
Their use (except in the case of <code>seq</code>) would require some |
Their use (except in the case of <code>seq</code>) would require some |
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kind of assurance on the part of the programmer that what they're doing |
kind of assurance on the part of the programmer that what they're doing |
Revision as of 05:56, 11 August 2022
A colleague [...] asked me today whether I know how to use unsafePerformIO
safely. And I realized I have no idea.
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
),
- breaks equational reasoning (
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.
unsafe
is also a keyword which can be used in a foreign import declaration.
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