Musical-X

Musical-X is an esoteric programming language whose source code consists entirely of music, invented by User:Zzo38.

You can only play one note at a time and rests are ignored. The first note indicates what key it is written in (it must be a major key). The commands exist between every 2 adjacent notes and depend on the interval between them, compound intervals are the same as simple intervals, and they are all considered to be notes in the major key (if they aren't, both the first and second note of the command are rounded up, so that you can play minor keys as well if you prefer). Unisons or octaves (simple or compound) are ignored as if they were only a single note, rather than two equivalent notes.

There are many infinite tapes as in Brainfuck with values 0-255, each tape has a separate pointer, and each tape is named with one note. The initial tape is the note at the beginning of the program.

Examples
(Note: These examples are given using the PLAY syntax in QBASIC.)

Program to copy input to output until chr(0): "l8mlo2c16p16c16f.fl32e-e-e-e-"