I am cross-posting this message to several lists. I had learned the trick before the documentation was updated. It seems I have used a very unreliable trick. And the "use castToSTUArray" suggested alternative is a really poor one since I am not using arrays at all. Who can suggest a way to cast from Float to Word32 and Double to Word64 using ghc? The actual task is that I need to write out the Float as a little endian sequence of four bytes and also be able to read it back in. The writing and reading are done in Put and Get monads to ByteString (from the "binary" package). The alloca/poke/peek work around I have looks like castWord32ToFloat :: Word32 -> Float castWord32ToFloat x = unsafePerformIO $ alloca $ \p -> poke p x >> peek (castPtr p) castFloatToWord32 :: Float -> Word32 castFloatToWord32 x = unsafePerformIO $ alloca $ \p -> poke p x >> peek (castPtr p) The unsafeCoerce trick that is no longer working looks like: castWord64ToDouble :: Word64 -> Double castWord64ToDouble (W64# w) = D# (unsafeCoerce# w) castDoubleToWord64 :: Double -> Word64 castDoubleToWord64 (D# d) = W64# (unsafeCoerce# d) Any ideas? Or is the alloca trick the only way to do this? Chris Ian Lynagh wrote:

Hi Chris,

On Sun, Sep 21, 2008 at 05:37:33PM +0100, Chris Kuklewicz wrote:

...

Also, I tried two tricks: (D# x) <-> (W64# x) which works fine (F# x) <-> (W32# x) which produced garbage, so I had to replace it with alloca/poke/peek.

This isn't supported, and I suspect is the cause of the -fasm problems.

Please see http://hackage.haskell.org/trac/ghc/ticket/2209 for more details and suggested alternative.

Thanks Ian