var axiom = "F-G-G";

var sentence = axiom;

var len;

​

var rules = [];

rules[0] = {

  a: "F",

  b: "F-G+F+G-F"

}

rules[1] = {

  a: "G",

  b: "GG"

}

​

function generate() {

  len *= 0.5;

  var nextSentence = "";

  for (var i = 0; i < sentence.length; i++) {

    var current = sentence.charAt(i);

    var found = false;

    for (var j = 0; j < rules.length; j++) {

      if (current == rules[j].a) {

        found = true;

        nextSentence += rules[j].b;

        break;

      }

    }

    if (!found) {

      nextSentence += current;

    }

  }

  sentence = nextSentence;

  createP(sentence);

  turtle();

​

}

​

function turtle() {

  background(51);

  resetMatrix();

  translate(width / 2, 20);

  rotate(radians(30));

  stroke(255, 100);

  for (var i = 0; i < sentence.length; i++) {

    var current = sentence.charAt(i);

    if (current == "F" || current == "G") {

      line(0, 0, 0, len);

      translate(0, len);

    } else if (current == "+") {

      rotate(angle);

    } else if (current == "-") {

      rotate(-angle);

    }

  }

}

​

function setup() {

  createCanvas(400, 400);

  angle = radians(120);

  len = height;

  background(51);

  createP(axiom);

  turtle();

  var button = createButton("generate");

  button.mousePressed(generate);

}