22. Refinements: part 1

In this multi-part lesson, we are going to write a complete program to solve problems of increasing complexity. For each lesson, I will present a tentative solution that will contain one mistake. Try to find it before moving on to the next lesson.

22.1. A simple problem

Let us start by considering a simple problem: having Reeborg go around his world once and stop when it is back at its starting point. In concrete terms, select world Around 1. We have done something like this before, when we introduced the front_is_clear() test. Here’s the outline of a solution which supposes that Reeborg carries at least one token at the beginning:

1. Put down a token to mark the starting (and ending) point.
2. Move forward until facing a wall.
3. Turn left when facing a wall.
4. Repeat steps 2 and 3 until we find the token we had put down.

Take you time to think about the above algorithm. Then, consider this solution in code:

put("token");
while ( !token_here() ){
    if (front_is_clear()){
        move();
    } else {
        turn_left();
    }
}

Your turn!

Take the time to think about what the above program instructs Reeborg to do before trying to run it. Can you find a problem with the proposed solution?