I'm working with a C++ application library, of the sort where you instantiate a subclass of the library object and it dispatches your functions on receipt of various events. With multiple OS threads, by the way. This works all right so far, with some C++ boilerplate and Haskell FunPtrs created via the foreign "wrapper" option, but I am not crazy about marshalling the application data, to get it to the C++ object and back to my application functions. So, I'm wondering if the way I'm trying to thread application data through the C++ layer is reasonably fool-proof - I mean, empirically it works in a simple test, but are there going to be storage issues, etc.? Is there a better way to do it? Briefly, - my callbacks AppData -> CPlusObjectPtr -> P0 ... -> IO Pn - the FunPtr inserted into C++ object FunPtr (CPlusObjectPtr -> P0 ... -> IO Pn) ... i.e, I apply the AppData parameter first - I rewrite the C++ object's FunPtrs every time I update the application data (freeHaskellFunPtr prior values.) I'm just not sure where AppData lives while it's referenced in a FunPtr via partial application, if there might be multiple copies, etc. thanks! Donn Cave, donn@avvanta.com