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// the output of the productions 
// will be a list of line segments
var lines = [];

// simple turtle graphic system to create these lines:
function turtle_new() {
	return {
		p: new vec2(),
		d: new vec2(1, 0),
		a: Math.PI / 3,
	};
}

function turtle_copy(t) {
	return {
		p: t.p.clone(),
		d: t.d.clone(),
		a: t.a * 2/3,
	};
}

function turtle_render(t, str, lines) {
	var i = 0;
	while (i <= str.length) {
		var c = str.substring(i, i+1);
		if (c == "F") {
			// add a line start-point at the turtle location:
			lines.push(t.p);
      // move the turtle forward (make a new point):
      t.p = t.p.clone().add(t.d);
			// add the line end-point at the new turtle location:
			lines.push(t.p);
    } else if (c == "+") {
			// turn turtle:
			t.d.rotate(t.a);
    } else if (c == "-") {
			// turn turtle:
			t.d.rotate(-t.a);
		// push/pop machine:
    } else if (c == "[") {
			// create a copy of the turtle:
			var turtle1 = turtle_copy(t);
			var str1 = str.substring(i+1);
			i = i + turtle_render(turtle1, str1, lines);
    } else if (c == "]") {
			return i;
		}
		i = i + 1;
	}
	return i
}

// now the L-system:

// start pattern:
var str = "F";

// production rules:
var rules = {
	F: "F+F--F+F",
};

// apply production rules:
function apply_production_rules(str) {
	var res = [];
	for (var i=0; i<str.length; i++) {
		var c = str.substring(i, i+1);
		if (rules[c] !== undefined) {
			res.push(rules[c]);
    } else {
			res.push(c);
		}
	}
	str = res.join("");
  
  // and develop these into the lines:
  lines = [];
  turtle_render(turtle_new(), str, lines);
  
	return str;
}

// rendering & interaction:
turtle_render(turtle_new(), str, lines);

function mouse(e, p) {
  if (e == "down") {
    if (str.length > 1000) {
      // reset
      str = "F";
    } else {
	    str = apply_production_rules(str);
    }
  }
}

function draw() {
  write(str);
	
  // get min & max extents of the shape
  // in order to automatically scale to fit on screen
  var a = lines[0].clone();
  var b = lines[0].clone();
  for (var l of lines) {
    a.min(l);
    b.max(l);
  }
  b.sub(a);
  draw2D.translate(0.1, 0.1)
    .scale(0.8/Math.max(b[0], b[1]))
    .translate(a.negate());
  
  // now draw lines:
  draw2D.lines(lines);
}


            
          
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