If you think about, it controlling live music is far more difficult than controlling a web browser.
If you think that reactive programming in a web browser is difficult then think again - this is really really easy compared to control a live-gig performance setup with two or three musicians, a dozen synthesizers and half a dozen computers.
In the 2014 Strangeloop keynote Our Shared Joy of Programming Carin Meier and Sam Aaron had drones dancing to live music (look at the video 43 minutes from the start). This is Bigtime badass reactive programming and is something far more difficult than anything “reactive” done in a browser. This is real-world objects reacting in real-time to messages.
One of the most difficult control problems I can imagine involves an orchestra of 50 musicians.
An orchestral musician has two main inputs, ears and eyes, the conductor has an advance gesture control device, a wooden stick which predates the Internet of things and works remarkably well. It boots instantly, requires no cloud storage, and doesn't need firmware updates, and doesn't nag you every day about not having been backed up.
The orchestra is controlled by waving the stick.
Listening to sound from multiple instruments and transcribing it accurately is something no computer can yet do with any accuracy.
Timing in musical performance is critical, delays of more than a few milliseconds are noticeable, tempo shifts not so important, provided all the musicians change tempo at the same rate.
Music as a control problem is terribly difficult - it pushes our understanding of interfaces to the limit.
This is why the methods and the software designed for live performance is worthy of study - I've started looking at this in some detail and I think there's a lot we can learn from it, and that this should influences how we design software and how we interact with things.
This is particularly relevant as we move into a world of the Internet Of Thinsg. Is there really a better way of conducting an orchestra than waving a bit of wood, or has thousands of years of evolution and experimentation resulted in the perfect control device - a stick?
So the problem is intrinsically parallel, distributed and soft real-time.
“Auugh you're thinking,” are there any programming languages designed to be intrinsically parallel, distributed and soft real-time?”
So the match between Erlang and Music control is pretty obvious - it's just that Erlang has been used for the soft real-time control of distributed telecommunication systems and not orchestras.
I thought I'd take a look at how some systems designed for live performance look.
Several things are immediately apparent (and this is based on observation of three systems, Sonic Pi SuperCollider and Pure Data - to start with the controls have a declarative feel - the interfaces are simple, and these are build from many components which operate in parallel.