Well, if you know anonymous function, it should be easy to understand what happens. Functions are first-class objects here. Q is a procedure that takes an arbit

Well, if you know anonymous function, it should be easy to understand what happens. Functions are first-class objects here. Q is a procedure that takes an arbitrary procedure. It's not that you run the procedure. In fact, it's another way around, you want to say something about the source code of the function, not the result of applying it.