ashley:

I would like to start a discussion on the role of unsafe functions in Haskell:

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, unsafePreservingMatrix, unsafeRenderPrimitive

perhaps also

unsafeForeignPtrToPtr :: ForeignPtr a -> Ptr a (which is already under Foreign.*) hGetContents :: Handle -> IO String (which is lazy rather than unsafe per se)

* Do you use these, and what for?

unsafePerformIO, for making pure functions from foreign library bindings. unsafeInterleaveIO, less common, sometimes used to implement low level Chan-like constructs using foreign IO primitives.

* Is there safe functionality that can currently only be obtained with them?

Foreign library bindings, as in Text.Regex, use unsafePerformIO extensively.

* Do you think they should be standardised, and how?

I'm thinking the unsafe functions should be moved from System.IO.Unsafe and elsewhere to Unsafe, similar to Foreign.*, to better separate them from "real Haskell" conceptually. Also, I would add:

unsafeCoerce :: a -> b

Something like: Unsafe.IO Unsafe.ST ? This came up recently when discussing why peek and poke aren't 'unsafe' but Data.Array.Base.unsafeRead/Write are. It would make it easier to control the system in program like lambdabot, which evaluate arbitrary user code, and thus need to restrict the namespace to a trusted base that can't contain any unsafe* functions. Checking that functions (particularly Array) don't export anything unsafe was a bit tedious. -- Don

Am Mittwoch, 26. April 2006 01:02 schrieb Ashley Yakeley:

I would like to start a discussion on the role of unsafe functions in Haskell:

[...] unsafePreservingMatrix, unsafeRenderPrimitive [...]

These two functions are not "unsafe" in the sense the other functions are. The prefix only indicates that the action passed to them should not throw an exception. Cheers, S.