Difference between revisions of "Unsafe functions"

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.

Unsafe functions can break:

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.

@@ Line 1: / Line 1: @@
+<div style="border-left:1px solid lightgray; padding: 1em" alt="blockquote">
+A colleague [...] asked me today whether I know how to use <code>unsafePerformIO</code> safely. And I realized I have no idea. [...]
+<small>[https://discourse.haskell.org/t/using-unsafeperformio-safely/4146 Richard Eisenberg.]</small>
+</div>
+<sub> </sub>
 There are a number of '''unsafe functions''' in the libraries.
-* <hask>unsafePerformIO</hask>
+* <hask>unsafePerformIO :: IO a -> a</hask>
-* <hask>unsafeInterleaveIO</hask>
+* <hask>unsafeInterleaveIO :: IO a -> IO a</hask>
+* <hask>unsafeInterleaveST :: ST s a -> ST s a</hask>
+* <hask>unsafeIOToST :: IO a -> ST s a</hask>
+* <hask>unsafeIOToSTM :: IO a -> STM a</hask>
+* <hask>unsafeFreeze</hask>, <hask>unsafeThaw</hask>
+* <hask>unsafeCoerce# :: a -> b</hask>
+* <hask>seq :: a -> b -> b</hask>
+Unsafe functions can break:
+* type safety (<code>unsafeCoerce#</code>, <code>unsafePerformIO</code>),
+* [https://okmij.org/ftp/Haskell/index.html#lazyIO-not-True equational reasoning] (<code>unsafeInterleaveIO</code>),
+* or [http://en.wikipedia.org/wiki/Parametricity parametricity] (<code>seq</code>).
+Their use (except in the case of <code>seq</code>) would require some
+kind of assurance on the part of the programmer that what they're doing
+is safe.
+<code>unsafe</code> is also a keyword which can be used in a [http://haskell.org/haskellwiki/Performance/FFI foreign import declaration].
 {{stub}}
+[[Category:Idioms]]