let current = "A";

​

function setup() {

  createCanvas(640, 160);

  background(255);

  noLoop();

​

  // 9 generations

  for (let i = 0; i < 9; i++) {

    generate();

    // Render text to canvas

    textSize(16);

    textFont("courier");

    text(i + ": " + current, 4, 20 + i * 16);

  }

}

​

function generate() {

  let next = "";

  for (let i = 0; i < current.length; i++) {

    // For every character of the current sentence

    let c = current.charAt(i);

    //{!5} Apply the production rules A->AB, B->A

    if (c == "A") {

      next += "AB";

    } else if (c == "B") {

      next += "A";

    }

  }

  // Save the next generation

  current = next;

}

​