Very cool. I dug up an unfinished Lilypond arrangement that I'd been working on in 2008 and pasted it in and everything worked perfectly the first time.
I think if this had existed back then, the much-faster feedback loop would have helped me finish it. :)
Very neat indeed! Similar tools have done a lot to make TeX more accessible, so it makes sense that this also benefits lilypond.
I've started work on a project of my own that will do online rendering of lilypond (rather different design objectives from yours, though). I've been worrying a bit about resource consumption of frequent renders, and your application is occupying a rather extreme point there. Do you have any data about this already?
It would be really neat if I can export to a MIDI. Do you reckon that's easy to do for you? Lilypond in the back is storing this data in abc format right?
Separately, a question, which you guys might know how to solve:
How can I convert a PDF music sheet to a MIDI? I.e., does there exist a music-sheet to digital-music converter? The pdf in question I want to convert is not a scanned copy, it's been digitally produced by some other program (I don't know which program)
Someone requested MIDI and other exports at https://github.com/hacklily/hacklily/issues/2 and I'll try to tackle soon. Hacklily already makes MIDI available (for playback), so it's a matter of actually exposing that.
There are solutions for converting sheet music images to MusicXML/Finale/etc., but I haven't had good results with any of them.
I think if this had existed back then, the much-faster feedback loop would have helped me finish it. :)