Chapter 8: Using undefined characters in L-systems

[sidwellr]

In the presentation of how L-systems translate into turtle graphics commands, you might want to point out that characters not defined as turtle commands are simply ignored. This is often used in L-systems described in The Algorithmic Beauty of Plants and other L-system tutorials, so probably deserves mentioning.

On the other hand, mentioning this may be confusing without an example, which is probably more than you want to do. Perhaps that is why you omitted it! If so, just ignore this.

[sidwellr]

I watched the L-system video linked at the beginning of the online version of the book. It emphasizes the need to copy undefined characters without modification during L-system generation. This is not mentioned in the book; indeed the generate function on page 430 just drops undefined characters. (The sketch linked for Example 8.9 does copy undefined characters as it should.)

To clarify: undefined characters should be copied to the new string during the L-system generation process, but ignored by the turtle. The book doesn't address what should happen with undefined characters.