Quoth "Kees Bleijenberg"
My program creates a Windows dll. The calling program calls a function with strings as parameters. Works fine.
I want to add a extra parameter. This extra parameter is a callback: a function Int -> Int: stdcall. In Haskell I want to call this function. So I have to convert the pointer to a (formal) Haskell function.
In the examples for the FFI, Haskell provides the callback. I need an example or documentation.
It's unclear to me whether the Haskell program initially chooses the function and creates a pointer to it, or that happens in C/C++. In the former case, I think Foreign.StablePtr serves that purpose. In the latter case, Haskell will receive the function as something like FunPtr (CInt -> CInt), and you need a "dynamic" foreign function to convert the pointer, like foreign import ccall "dynamic" iiPtrStub :: FunPtr (CInt -> CInt) -> (CInt -> CInt) That's lightly documented in the library docs under Foreign.Ptr. Donn