Before considering a slightly more complex example, let’s review the preceding example:
def go_home(): if not at_goal(): move() go_home() # now do it! go_home()
Now, remember how I explained that when a function is called, we can think of it as replacing the function call by the body of that function. By this, I mean that this instruction:
if not at_goal(): move() go_home()
Let’s assume that the first time we execute these instructions, at_goal is false and hence not at_goal() is true ... like it was for world Home 1. In this case, the above calls to move and go_home() are executed, and the above code is equivalent to:
We can now replace the call to go_home() by its definition:
move() if not at_goal(): move() go_home()
and could, in theory, keep going like this forever, always replacing the call to go_home() by its definition.
However, we don’t want that as we want things to end eventually ... which they do fortunately for world Home 1. In that case after a second move(), at_goal() would be true and and the if statement would be ignored. Thus, the code in this case is equivalent to:
It is really important that you understand the above explanation before going any further. So, make sure to read it again if necessary as we are going to consider a slightly trickier example.
Consider the program below:
def go_home(): if not at_goal(): move() go_home() turn_left() # now do it! go_home()
Think about it
Try to figure out what it does before trying to have Reeborg execute it. An explanation follows in the next lesson.