Re: Global variables?

Nick Name wrote:

On Fri, 31 Jan 2003 07:47:43 +0000 Glynn Clements wrote:

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The usual fudge is:

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import IORef import IOExts

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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