Turtle examples for loops and variables, or even something else
What your system is missing, actually, seems to be a feedback mechanism in which the turtle can "sense" something about the world it is in. If it, for example, could sense edge walls, then it could use that sense for conditional constructs. In Karel the Robot and its successors (Karel J Robot, Monty Karel, ...) there are a number of things that a robot can sense such as walls and "beepers". 

while (karel.frontIsClear())... 

If you can have multiple turtles then one turtle sensing something about another is another possibility for feedback. 

But, until you get something like that (sensing about the world) you can probably only write conditional and looping constructs based on stored information in the program itself, such as counters.