title: How to create a simple l-system in Processing
body: <p>I want to create a simple l-system in Processing. I want to change every letter 'A' to 'AB' and every letter 'B' to 'A', starting with 'A'.</p>
  
  <p>The result should look something like this:</p>
  
  <pre><code>A →
  AB →
  ABA →
  ABAAB →
  ABAABABA → etc...
  </code></pre>
  
  <hr>
  
  <p>(P.S. I don't know much about processing)</p>