Here's my situation:

I would like to call ffmpeg's av_free_packet function:

// avformat.h
static inline void av_free_packet(AVPacket *pkt)
{
  if (pkt && pkt->destruct)
    pkt->destruct(pkt);
}

But unfortunately this function is static inline, and so doesn't really appear in the linked library.

However, it is a very simple function, which I could reimplement in Haskell. And that's what I can't figure out how to do. Here's a partial attempt (.hsc):

av_free_packet :: Ptr AVPacket -> IO ()
av_free_packet pkt =
  when (nullPtr /= pkt) $ do
    destruct <- (#peek AVPacket, destruct) pkt :: IO (FunPtr (Ptr AVPacket -> IO ()))
    when (nullFunPtr /= destruct) $ funPtrToFun destruct pkt

funPtrToFun :: FunPtr a -> a
funPtrToFun = ?

For now I could resort to implementing this function in C (by just calling the original), but it seems to me that calling function pointers should be possible somehow..

c haskell ffi
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