On Monday 22 July 2002 12:33 pm, Simon Marlow wrote:
The second seems to require this bit of weirdness.. myNewForeignPtr :: Ptr a -> (ForeignPtr a -> IO ()) -> IO (ForeignPtr a) myNewForeignPtr p fin = do newfp <- newForeignPtr p (return ()) addForeignPtrFinalizer newfp (fin newfp) return newfp
You can do this more easily using fixIO:
myNewForeignPtr p fin = do fixIO (\fp -> newForeignPtr p (fin fp))
Thanks, neat (I think:-). I wonder if I might indulge myself with another stupid question related to this, that is, why make the distinction between Ptr and ForeignPtr at all? By definition a ForeignPtr has a non-zero number of finalisers and Ptr has no finalisers. Couldn't you just allow ForeignPtr's to have no finalisers and dispense with Ptr alltogether? Then you could just add finalisers as required rather than converting between types. It seems that when making a foreign binding you have to make what seems (to me) an arbitrary choice between Ptr and ForeignPtr arguments. I don't really understand the reason for this extra complexity. Regards -- Adrian Hey