So, I watched the whole 17-minute screen cast. It turns out that "impromptu" is some kind of LISP environment with OpenGL and music-synthesizer bindings. I sat

So, I watched the whole 17-minute screen cast. It turns out that "impromptu" is some kind of LISP environment with OpenGL and music-synthesizer bindings. I sat there watching typing for a few minutes, wondering when he was going to hit "compile" and demonstratethe output of his program-in-progress, then suddenly I noticed that the soundtrack was changing as he edited the source. Colour me impressed.