Study existing GPLv3 licensed code while working on my own project

Question

I plan to write a toy interpreter for a programming language as a hobby project hosted on GitHub. The official implementation of the language is licensed under GPLv3. I have read some of its code to study how the parser works. But of course I won't copy or use any single line of its official implementation. Nor will I put my hobby project in any commercial use.

My questions are:

1. Can I use a different license for my own project?
2. Do I need to reference the official implementation somewhere in my project?

Answer 1

1. Yes, you can use.
2. If you are not using it at all, no, but as good practice you should refer your inspirations.

Also, I would like to highlight what you said about copying code, it's a tight line because you are getting inspired by that code. Just take caution about how you write the code, and don't fall in a copyright problem!