Joe Armstrong - Erlang and other stuff

Connecting Erlang to the SonicPi

Last September after giving my keynote at StrangeLoop I bumped into my old friend Sam Aaron. As usual he was bubbling over with enthusiasm, he'd been making a music program for kids Sonic Pi which interested me.

I'm interested in all things musical and especially making noises with computers so I was _very_ interested in Sonic Pi.

My first thought was “how can I control Sonic Pi from Erlang?” -- with Sam at hand this turned out to be really really easy.

“All you have to do,” said Sam “is open UDP port 4557 and send it an OSC message.”

“What message?” I asked.

"\run code $string" said Sam. Where $string is whatever you would have typed into the Sonic Pi control window.

“That's easy,” I thought, and it was. All I needed was a library to convert Erlang terms to OSC messages. After a little searching I found a library at erlang-osc.

The rest was easy.

I'd completely forgotten about this until earlier today when @WadeMeadling tweeted me asking if the code was documented anywhere. Well it wasn't and now it is.

I've put the code up at sonic_pi_inteface it's been tested with sonic Pi version 2.0 and seems to work.

# On the Sonic Pi Interface

I'd now like to take a moment and heap praises upon the design of Sonic Pi. It literally took me about ten minutes to interface Erlang to Sonic Pi.

Actually this is not quite true It took me ten minutes after Sam had explained how the interface worked - he had not documented the interface, assuming that nobody would wish to remotely control the program.

The interface is simplicity itself. Open a UDP port (in this case port 4557) and send it a fragment of Ruby (as an OSC message). Would that all programs were that easy to interface.

I have had the misfortune to interface Erlang to the Apple Core-audio and Core-midi interfaces - now this (interfacing to Core-audio) is not for the faint hearted.

Applications using core audio must be liked in memory to the core audio framework, a practice which is bizarre and which makes interfacing to languages that do not have the memory layout conventions of objective-C a pain.

This (the interfacing) harks back to the old arguments of “shared memory” verses “message passing” concurrency. Linking things in memory and using callbacks is painfully difficult and highly error prone.

This practise (shared memory) comes from the days when efficiency _was_ a problem, when we had computers with MHz clocks and tens of KBytes of memory. Those days are long gone.

Using a message passing, interfacing to Sonic Pi was pure joy. Open a port, send it a message, done. Easy.

If I were defining an audio API I'd be able to say:

piano ! {play_note, C}

From my favorite programming language (Erlang) and it would just work.

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