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So... if I'm not actually using lazyness for anything, would it do any harm to change Double to Double# in the Haskell source code? Or is there some reason why this would be undesirable? (The source is carefully constructed

Well, you'd need -fglasgow-exts for it to even compile. Other than that, you'd have to use all primitive operations and you might well be preventing the compiler from doing useful optimizations. But this is really a question for the Simons or other folks who actualy understand the GHC internals.

Hmm... that doesn't sound like such a hot idea...