Difference between revisions of "Unsafe functions"

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.

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 14: / Line 14: @@
 * <hask>unsafeIOToST :: IO a -> ST s a</hask>
 * <hask>unsafeIOToSTM :: IO a -> STM a</hask>
-* <hask>unsafeFreeze, unsafeThaw</hask>
+* <hask>unsafeFreeze</hask>, <hask>unsafeThaw</hask>
 * <hask>unsafeCoerce# :: a -> b</hask>
 * <hask>seq :: a -> b -> b</hask>
-Unsafe functions can break type safety (unsafeCoerce#, unsafePerformIO),
+Unsafe functions can break:
-interfere with lazy IO (unsafeInterleaveIO), or break [http://en.wikipedia.org/wiki/Parametricity parametricity] (<code>seq</code>).
+* type safety (<code>unsafeCoerce#</code>, <code>unsafePerformIO</code>),
+* [https://okmij.org/ftp/Haskell/index.html#lazyIO-not-True breaks equational reasoning] (<code>unsafeInterleaveIO</code>),
+* or break [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