What I've done has all been ad-hoc logic to build melodies out of patterns and whatnot, as opposed to an ML-style algorithm that learns from input data. That said, here are some samples:

a jazz chiptune: https://fenomas.com/2017/12/advent-17/

Zelda as gypsy jazz: https://fenomas.com/2017/12/advent-13/

vaguely fuguelike: https://fenomas.com/2017/12/advent-18/