I realised the example above is rather poor. Here’s the output of a more explanatory example of reactive Elm in litvis.
Alex Kachkaev gave a talk at Elm-Europe this year literate elm (in the context of building a system for literate visualization):
Summary:
https://www.youtube.com/watch?v=D_KwyxSjRjw
Full talk:
https://www.youtube.com/watch?v=K-yoLxnm95A&list=PL-cYi7I913S-VgTSUKWhrUkReM_vMNQxG&index=7&t=0s