Re: [Haskell-cafe] GHC optimizations and unsafePerformIO - Was: Data.Typeable TypeRep Ord instance.

On 1 Jan 2011, at 12:38, Andreas Baldeau wrote:

Thinking about this there might be one problem:

Without having looked further into this I think perfomance might not be as expected. Using unsafePerformIO affects ghc's optimzations, doesn't it?

So I wonder if it's a good idea (from a performance point of view) to use this.

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2010/12/30 Andreas Baldeau :

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instance Ord TypeRep where compare t1 t2 = compare (unsafePerformIO (typeRepKey t1)) (unsafePerformIO (typeRepKey t2))

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typeRepKey :: TypeRep -> IO Int typeRepKey (TypeRep (Key i) _ _) = return i

So the question is, if ghc could transform this to simply compare the keys throwing away unsafePerformIO and return.

Wouldn't a much better plan simply be to take typeRepKey out of the IO monad? Bob