var is_even := index % 2 == 0var poly_partial := 
needs to be
var is_even := index % 2 == 0
var poly_partial := 
A similar error snuck into the _add_connection function in the full code reference.
But more importantly, the code in this lesson uses spaces even though the code in the previous lesson used tabs. Godot actually enforces using tabs or spaces and counts mixing them as an error.
The code works fine once these two problems are fixed.
Thanks for reporting this one! Seems like a remnant of issues with the previous text editor the platform used. It messed up code formatting. I'm off right now but I'm logging it to address when I'm back to work.
I just updated the chapter. Now, all code examples should use spaces; our script to highlight GDScript converts tabs to spaces at the moment.
Please let me know if you have any other issues. Unfortunately, when we started using the platform, we had trouble with the text editor, which is solved now the devs changed the technology for us. I tried to fix all the issues people reported at the time, patched dozens of lessons, but there are some leftover problems to fix, like the mixed tabs and spaces.
And thanks for taking the time to report the issue!
If you find any similar one, you don't even need to specify the faulty line of code or block; a one-liner to indicate that a lesson has a code formatting issue is all I need to address the problem.