Write a Forth. ;)

Or a Lisp and let the user face them instead.

Forth seems easier to do over a weekend, though.

There's even a recipe posted in a couple of comments here:

https://news.ycombinator.com/item?id=13082825

I followed that guide to implement a simple FORTH-like system in golang:

https://github.com/skx/foth

As I was following the implementation recipe I broke it down into "educational steps". Although it isn't a true FORTH it is pretty easy to understand and useful enough to embed inside other applications.

Now and again I consider doing it again, but using a real return-stack to remove the hardcoded control-flow words from the interpreter, but I never quite find the time.

Definitely easier; it has no structure at all, it's all in your head/stack.

https://github.com/codr7/fipl