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In 2009, I made Velato, an esolang where code is written in pitch values (https://github.com/rottytooth/Velato) encoded as MIDI files. So sort of the opposite of writing algorithmic music (where the human programmer writes music to satisfy conditions of the program). Before switching to LilyPond, I'd used GUIDO with a GUIDO-to-MIDI generator, but it was always awkward. Part of the challenge is that notes can be sounded simultaneously to make the score work better musically, but still need to appear in the correct sequence in the MIDI file for the program to succeed; something that LilyPond handles correctly. There's a transparency to how LilyPond functions that is not always there with programs that try to be "helpful" and clean-up or rearrange information.