function setup() {
  createCanvas(720, 400);
  textAlign(CENTER, CENTER);
  textFont('monospace');
  textSize(fontSize);
  generatingTokenColor = color(200,250,255);
  newTokenColor  = color(240);

  synth = new p5.PolySynth();
  sloop = new p5.SoundLoop(soundLoop, 0.7);

  playPauseButton = createButton('Play/Pause');
  playPauseButton.position(width - 2*playPauseButton.size().width, height - 2*playPauseButton.size().height);
  playPauseButton.mousePressed(togglePlayPause);
  stepButton = createButton("Step");
  stepButton.position(2*stepButton.size().width, height - 2*stepButton.size().height);
  stepButton.mousePressed(stepSoundLoop)
}
Example: Fractal Music
Generate a fractal pattern of music using L-Systems. 

We begin with an initial sequence of tokens, and use a programmer-
defined set of rules to generate new tokens. Here, we apply the rules:
A -> C, F, E
C -> G, E
E -> C, G
F -> A, C
G -> E, F, C
to each token in existing sequences to generate new sequences. The 
tokens used here are plain note names from a fixed octave. Note durations 
are selected randomly from a palette of "nice" durations.