  With the goal of building a system capable of controllable symbolic music
loop generation and editing, this paper explores a generalisation of Masked
Language Modelling we call Superposed Language Modelling. Rather than input
tokens being known or unknown, a Superposed Language Model takes priors over
the sequence as input, enabling us to apply various constraints to the
generation at inference time. After detailing our approach, we demonstrate our
model across various editing tasks in the domain of multi-instrument MIDI
loops. We end by highlighting some limitations of the approach and avenues for
future work. We provides examples from the SLM across multiple generation and
editing tasks at https://erl-j.github.io/slm-mml-demo/.
