On 7/20/06, Evan Martin <[EMAIL PROTECTED]> wrote:
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?
Yes. You can use any Storable with FFI functions, as far as I know. StablePtr is explicitly designed for this purpose, allowing you to "export" an object to the FFI while keeping the GC apprised of its use by external code.
/* 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 ()
Oh, right. Try: type CallbackData = StablePtr (CallbackData, DataStructure) type Callback = CallbackData -> IO () foreign import ccall register_callback :: FunPtr Callback -> CallbackData -> FunPtr Callback -> IO () You get that FunPtr by the import/export trick described by Anatoly or you can just construct the FunPtr in main or an unsafePerformIO CAF. (We need a constructor syntax for top-level objects requiring IO!) -- Taral <[EMAIL PROTECTED]> "You can't prove anything." -- Gödel's Incompetence Theorem _______________________________________________ Haskell mailing list Haskell@haskell.org http://www.haskell.org/mailman/listinfo/haskell
