> I wonder if what is needed is a kind of "side program" that one could use to annotate the main program in very precise ways and ask questions of its execution

> I wonder if what is needed is a kind of "side program" that one could use to annotate the main program in very precise ways and ask questions of its execution, or to produce maps or timelines of aspects of its behavior. But not via interactions with a GUI, although those are useful too, but as actual code that lives alongside the real code, using the same language. Something a bit like a souped-up, visual dtrace, perhaps. I don't know what is already out there like that, but I would love to see work in that direction. This is a great idea. I find it ironic that so much of programming consists of 'simulating the computer' in one's head while sitting in front of a computer. I would love to be able to visualize many things that a compiler does internally, for instance, to see how generic code looks when specialized in a certain context.