On 7/21/06, Taral <taralx@gmail.com> wrote:
On 7/20/06, Evan Martin <martine@danga.com> wrote:
The tricky part is that to pass in Haskell functions, I need to use the FFI "wrapper" import, which means I need to later free them. But the only place I can free them is within the "free" callback, and I've just discovered this isn't allowed!
free_fcn is normally a static function. It shouldn't need to free itself. I'm thinking something like:
type Callback = StablePtr (Callback, DataStructure)-> IO () foreign import ccall "wrapper" mkCallback :: Callback -> IO (FunPtr Callback) foreign export "free_fcn" free_fcn :: Callback
free_fcn sp = do (cb, ds) <- deRefStablePtr sp freeStablePtr sp freeHaskellFunPtr cb
Ah, I think I see. I hadn't looked at "export", but a static function does seem like what I want. But I also don't quite understand how the typing works out. For example, can you use StablePtr directly with FFI functions, or do they require you casting through Ptr? /* C code, as before but with a typedef for clarity */ typedef void (*Callback)(void*); void register_callback( Callback callback_fcn, void *callback_data, Callback free_fcn); -- importing this function. -- you had: type Callback = StablePtr (Callback, DataStructure)-> IO () foreign import ccall register_callback :: FunPtr Callback -> -- because mkCallback gives a FunPtr Ptr (Callback, DataStructure) -> -- or StablePtr? Callback -> -- but here don't we again need a FunPtr? IO ()