This rules! I could see myself losing a lot of time to this, especially if the recursive mechanic gets used more as you go further in (actually requiring you to go back and fix your previous solutions a lot). Can I ask how many levels there are? Made it to world 6 so far.
There are 6 Levels. For Level 6 you will have to go back and change some solutions.
Personally, I can't consistently beat Level 6, but I know that it's always solvable.
I was thinking of adding an endless mode, but then decided to release the game without it. The difficulty spike is just too hard to actually be fun.