Re: Global variables?

On 02-Feb-2003, Jon Cast wrote:

Claus Reinke wrote:

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It is the programmer's responsibility to verify that none of these problems matter in the particular case of usage. Since many advances in compiler technology tend to invalidate those verifications, it is almost impossible to guarantee safety in such cases

Even with sufficiently liberal use of {-# NOINLINE #-}?

Haskell Report, Appendix E (Compiler Pragmas): "An implementation is not required to respect any pragma".

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There you went.. into one of the many available traps in this mine-field:

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You argue that unallocated IORefs don't matter as long as "the" IORef is allocated before it is dereferenced. But that's just part of the problem - what about inlining globalVar, creating multiple IORefs?

{-# NOINLINE globalVar #-} :)

What about creating two copies of globalVar, neither of them inlined? A compiler could do that to improve performance on some architectures, e.g. by allowing the function to be called via a short jump instruction rather than a long jump instruction. -- Fergus Henderson | "I have always known that the pursuit The University of Melbourne | of excellence is a lethal habit" WWW: http://www.cs.mu.oz.au/~fjh | -- the last words of T. S. Garp.