On the GUI toolkit issue, I'd recommend combining gtk2hs (which is a thin wrapper around GTK) with Reactive Banana. GTK signals are isomorphic with Banana event

On the GUI toolkit issue, I'd recommend combining gtk2hs (which is a thin wrapper around GTK) with Reactive Banana. GTK signals are isomorphic with Banana events and GTK attributes are isomorphic with Banana behaviors. So you can connect up a button press signal from GTK to an Event, transform that event with data from some other behavior, and hence generate a new behavior which is connected to the GTK attribute of the text displayed in a text box. Your application logic is then expressed as the plumbing that pipes data from event sources to event and behavior sinks. This works well because the event plumbing is composable in ways that callbacks and state variables of native GTK aren't.