On Mon, Feb 03, 2003 at 09:20:03PM +1100, m v wrote:
>
> I do not understand the rational of the type of:
>
> newForeignPtr :: Ptr a -> FunPtr (Ptr a -> IO ()) -> IO (ForeignPtr
> a)
>
> suppose I have a c function
>
> foreign import ccall fooalloc :: Ptr Foo
>
> and another
>
> foreign import ccall foofree :: Ptr Foo -> IO ()
>
> now I want to combine fooalloc and foofree to create a Foreign pointer
> without wrapping foofree again, as in:
>
> foreign import "wrapper" mkfoofree :: FunPtr (Ptr Foo -> IO ())
>
> which I think counter productive - why should I import a function only to
> have to re-export it again !
You don't need to wrap it -- you can import its address with
foreign import ccall "&foofree" foofreeptr :: FunPtr (Ptr a -> IO ())
> previouse proposals did not require this - or am I missing something ?
>
> why should the finaliser be a foreign function ?
It's a long story, but it turned out that Haskell side finalizers are hard
to implement correctly in conventional single-threaded implementations.
After a long discussion on this list in October last year, SimonM came up
with a killer example:
http://www.haskell.org/pipermail/ffi/2002-October/000866.html
http://www.haskell.org/pipermail/ffi/2002-October/000910.html
For a summary of the discussion, see
http://cvs.haskell.org/cgi-bin/cvsweb.cgi/haskell-report/ffi/finalizers.txt
However, only Hugs implements this part of the spec at the moment.
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