Andrew J Bromage wrote:

G'day all.

On Fri, Jan 31, 2003 at 01:54:26PM -0600, Jon Cast wrote:

...

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.

As has been pointed out, there is no language requirement for a Haskell implementation to be "fully lazy". In particular, it is technically possible for an implementation to garbage collect globalVar and re-evaluate it on the next call.

So, the technique is implementation-dependent. Since Hughes' recommendation is equally non-portable, I don't see this as a serious problem in this case.

Haskell 2 should probably have a pragma controlling this.

IMO, that would be a good idea :)

Cheers, Andrew Bromage