turtle.js

var quads = [0, -90, 90, 180, -180];

function fortor(a) {
  // squares
  // var n = 20;
  // versus random
  var n = ~~(Math.random() * 400)
  return function(t) {
    return (t % n) ? a : quads.map(fortor);
  }
}

turtle(function(t) {
  return [fortor(0)];
});