Global variables?

[Ralf Hinze]

> Pavel G. Zhbanov wrote:
> > Is it even possible to make a "global variable" in Haskell?
> > If yes, how?
>
> The usual fudge is:
>
> 	import IORef
> 	import IOExts
>
> 	globalVar :: IORef Int
> 	globalVar = unsafePerformIO $ newIORef 0
>
> However, beware of creating more than one "global variable" of the
> same type. If you enable optimisation, common subexpression
> elimination may result in both names referring to the same IORef.

John Hughes wrote a nice pearl on the subject, see

	http://www.math.chalmers.se/~rjmh/Globals.ps

Cheers, Ralf