Difference between revisions of "Unsafe functions"
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| + | <div style="border-left:1px solid lightgray; padding: 1em" alt="blockquote"> |
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| + | A colleague [...] asked me today whether I know how to use <code>unsafePerformIO</code> safely. And I realized I have no idea. [...] |
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| + | <small>[https://discourse.haskell.org/t/using-unsafeperformio-safely/4146 Richard Eisenberg.]</small> |
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| + | </div> |
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| + | <sub> </sub> |
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There are a number of '''unsafe functions''' in the libraries. |
There are a number of '''unsafe functions''' in the libraries. |
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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: |
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| − | interfere with lazy IO (unsafeInterleaveIO), or break paramatericity (seq). |
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| + | * type safety (<code>unsafeCoerce#</code>, <code>unsafePerformIO</code>), |
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| + | * [https://okmij.org/ftp/Haskell/index.html#lazyIO-not-True equational reasoning] (<code>unsafeInterleaveIO</code>), |
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| + | * or [http://en.wikipedia.org/wiki/Parametricity parametricity] (<code>seq</code>). |
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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 |
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is safe. |
is safe. |
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| + | <code>unsafe</code> is also a keyword which can be used in a [http://haskell.org/haskellwiki/Performance/FFI foreign import declaration]. |
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Latest revision as of 12:27, 8 June 2023
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 -> aunsafeInterleaveIO :: IO a -> IO aunsafeInterleaveST :: ST s a -> ST s aunsafeIOToST :: IO a -> ST s aunsafeIOToSTM :: IO a -> STM aunsafeFreeze,unsafeThawunsafeCoerce# :: a -> bseq :: a -> b -> b
Unsafe functions can break:
- type safety (
unsafeCoerce#,unsafePerformIO),
- equational reasoning (
unsafeInterleaveIO),
- or 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.
This article is a stub. You can help by expanding it.