> I am using ghc-5.04 and a code like:
>
> with c ( \c' -> hPutBuf h c' (sizeOf c))
>
> fails with "Fail: Prelude.undefined" when "c" is a user defined type,
> such as a pair:
>
> instance (Storable at,Storable bt) => Storable (at,bt) where
> sizeOf (a,b) = sizeOf a + sizeOf b
> alignment (a,b) = max (alignment a) (alignment b)
> peek p = do a <- peek ((castPtr p):: Ptr at)
> b <- peekByteOff ((castPtr p):: Ptr bt) (sizeOf a)
> return (a,b)
> poke p (a,b) = do poke ((castPtr p):: Ptr at) a
> pokeByteOff ((castPtr p):: Ptr bt)
> (sizeOf a) b
sizeOf and alignment are not supposed to evaluate their arguments. You
might try making the definitions in your instance above a little lazier:
sizeOf z = sizeOf a + sizeOf b where (a,b) = z
alignment z = max (alignment a) (alignment b) where (a,b) = z
(feel free to use '~' if you prefer).
Cheers,
Simon
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