Global variables

[David House]

(CCing the list as this is of general concern.)

On 01/02/07, Yitzchak Gale <gale at sefer.org> wrote:
> Why is this unsafe? What could go wrong?

It could segfault due to the type safety properties that unsafePerformIO breaks:

import System.IO.Unsafe
import Data.IORef

ref :: IORef [a]
ref <- newIORef []

main = do
  writeIORef ref [42]
  val <- readIORef ref
  print (val :: [Char])

If you use the pragma you're forced to import unsafePerformIO and
hopefully check the haddock docs [1] where this issue is listed.

[1]: http://haskell.org/ghc/docs/latest/html/libraries/base/System-IO-Unsafe.html

-- 
-David House, dmhouse at gmail.com