Re: ForeignPtr's - why can't they be passed directly to foreignfunctions?

kahl@cas.mcmaster.ca wrote:

Brian Hulley wrote:

...

My other question is what happens if I want to have a function that takes more than one ForeignPtr as argument ie

foreign import ccall duma_test :: Ptr (Window a) -> Ptr (Window a) -> IO ()

test :: ForeignPtr (Window a) -> ForeignPtr (Window a) -> IO () test p q = withForeignPtr p (\p' -> withForeignPtr q $ duma_test p')

Is this the only way to achieve this? It seems a bit long-winded and possibly a bit inefficient...

I use:

\begin{code} {-# INLINE with2ForeignPtrs #-} {-# INLINE with3ForeignPtrs #-} with2ForeignPtrs :: ForeignPtr a -> ForeignPtr b -> (Ptr a -> Ptr b -> IO c) -> IO c with2ForeignPtrs f1 f2 m = withForeignPtr f1 (withForeignPtr f2 . m) \end{code}

\begin{code} with3ForeignPtrs :: ForeignPtr a -> ForeignPtr b -> ForeignPtr c -> (Ptr a -> Ptr b -> Ptr c -> IO d) -> IO d with3ForeignPtrs f1 f2 f3 m = withForeignPtr f1 (with2ForeignPtrs f2 f3 . m) \end{code}

Good idea!

...

foreign import ccall duma_init :: IO ()

^^^^

Any relation with duma.sourceforge.net ? ``D.U.M.A. - Detect Unintended Memory Access''

No - I just got it off the cover of a DVD! (after spending about a week wasting time trying to think of a name... :-) ) Thanks, Brian.