<script src="http://spelprogrammering.nu/simple.js">
function start()
{
  var axiom   = 'F';

  var rules   = {'F': 'F+F--F+F', 
                 '+': '+', 
                 '-': '-'};

  var actions = {'F': function() { turtle.move(length);     },
                 '+': function() { turtle.turnLeft(angle);  },
                 '-': function() { turtle.turnRight(angle); }};

  var iterations = 4;
  var angle      = 60;
  var length     = 5;

  var system = axiom;

  for (var i = 0; i < iterations; i++)
  {
    var currentLength = system.length;
    var newSystem = '';
    for (var u = 0; u < currentLength; u++) 
    { 
      newSystem += rules[system[u]]; 
    }
    system = newSystem;
  }
  
  for (var i = 0; i < system.length; i++)
  {
    actions[system[i]]();
  }
}
</script>