I've just finished the section 2 of the book _Crafting Interpreters_, and I wanted to upload it to github right away. Take a look at the source code. Beside the lox specification I've added:
The keyword until that is a variation of while loops (as in ruby). also
print is a function instead of a statement.
eval function that let's you eval source code in runtime.
I'll implement another language interpreter, this time using golang and with a syntax similar to ruby.