Have you ever tried implementing a language spec?

Recently I was reading through Safia(@captainsafia)'s post, where they dive into the JavaScript spec to discuss the implementation of the Array.prototype.filter function:

The fun of filter, according to the ECMAScript spec

Safia Abdalla ・ Jan 22 '20 ・ 4 min read

#javascript #spec #filter #array

Reading through the algorithm, I felt the urge to implement it. I guess I'm just programmed that way 😆

I didn't, though. I've thought many times that it would be a fun challenge to implement a language spec, and a great way to learn about language design and the choices made by the creators of my tools. But I still have never tried.

If you've tried, what was your experience like?
If you haven't tried, why does or doesn't it sound like fun? 🤔

(I'm asking specifically about implementing an existing language spec; creating your own sounds fun, too, but not the topic I'm introducing for discussion in this post 😄 another time, perhaps!)