Yes, I made my own AST. You know, it started as a parser, evolved into an interpreter :). But I will definitely talk to Andreas (creator of Nim) if using Nim AST would be an advantage.
At any rate, your language does look rather interesting, and I should thank you for your blog post. It has made me think about how the syntax of Rebol (which was unknown to me) could possibly inform a language designed to combine ideas from both Smalltalk and Lisp.
Smalltalk is quite lispish in many ways (closures, most stuff is an expression, simplicity etc). Rebol fascinates me - and I have only scratched its surface. For more on Rebol you should look at www.red-lang.org. Especially the stuff around the Parser DSL, like:
In terms of development toolkit and implementation then yes Red could/should be considered the "modern Rebol".
However in terms of the language (syntax & semantics) then Rebol 3 is definitely the "modern Rebol". Have a look at Ren/C for the new ideas and the very latest development of the Rebol 3 codebase - https://github.com/metaeducation/ren-c
You are ever so correct, sorry about that! I also would like to say that I am slightly "disappointed" that Red decided to stick so closely to Rebol. Personally I definitely don't find everything in Rebol to be so perfect. ;)