--- Peter Achten wrote:

Perhaps there is an interesting alternative that covers all GOOD points and has fewer BAD points.

Some pieces of library can be simplified if redefine: data WindowLSHandle ls ps = WindowLSHandle { wlsState :: ls , wlsHandle :: WindowHandle ls ps } as data WindowLSHandle ls ps = WindowLSHandle { wlsState :: MVar ls -- or IORef ls , wlsHandle :: WindowHandle ls ps } That let Object I/O to manage local state but simplifies implementation of WindowDevice (see WindowDevice.hs). There isn't need of fixIO and not need to use of build function. This also simplifies creation of modal dialogs and synchronous message passing. The current implementation uses unsafeTypeCast function which is not a good idea. In this implementation the type system is still complicated but my decision is just to skip type declarations and let compiler to resolve function types for me. In my experience with Object I/O I notice that type error is usually logical error. So types for me isn't a trouble. __________________________________________________ Do You Yahoo!? Yahoo! Tax Center - online filing with TurboTax http://taxes.yahoo.com/