Global variables?

[Jon Cast]

Nick Name <nick.name@inwind.it> wrote:
> On Fri, 31 Jan 2003 07:47:43 +0000
> Glynn Clements <glynn.clements@virgin.net> wrote:

> >  The usual fudge is:

> >  	import IORef
> >  	import IOExts

> >  	globalVar :: IORef Int
> >  	globalVar = unsafePerformIO $ newIORef 0

> I see in the documentation of unsafePerformIO that no one makes
> guarantees about the order in wich unsafePerformIO arguments are
> performed (especially they don't have to be executed BEFORE main), so
> this trick should not be adviced as a general practice; it should be
> pointed out that it works in GHC but could not work in other
> compilers.

English nit: I think you mean ``could fail in other compilers'': it's
not really impossible for the trick to work in other compilers than
GHC.

Otherwise, though, see my other post on this subject: unsafePerformIO
will perform its action when the variable is accessed, so you can't
write a Haskell program which differentiates between what any compiler
actually does and running the variable allocations before main.

> Vincenzo

> --
> Fedeli alla linea, anche quando non c'š Quando l'imperatore š
> malato, quando muore,o š dubbioso, o š perplesso.  Fedeli alla linea
> la linea non c'š.  [CCCP]

Jon Cast