We have gobs of RAM now, and these fast processors that are usually idle while you type and then suddenly strained when you compile. Why doesn't the IDE continually build parse trees as you type? They have to do some preliminary parsing already to do syntax highlighting. But with more of the compiler integrated you not only get more contextual help (see, for example, Visual Studio, which shows you in a tooltip the type of the argument expected for the function you're calling), but also an incredible boost in compile time.
(This seems obvious enough that someone would be doing research in it...)
