rx VS common-regex

I had a similar kind of idea for a long time, which I put into action a few weeks ago via a standalone transpiler of Emacs' rx macro to common regexp syntaxes.[0] I ended up getting interrupted and didn't completely finish it, but it generally works, though is probably riddled with edge cases.

The basic idea of rx is to use S-expressions to describe regular expressions, and my elevator pitch would've been to embed rx invocations in shell scripts using $(syntax), the main use case being something like sed invocations.

I still think it's a neat idea, and complex regular expressions tend to be hard to parse for humans.

[0]: https://github.com/sulami/rx

comparitor.insert("iyr", Regex::new(r"^(201[0-9]|2020)$").unwrap());

There are lots of number parsing.

I would enable both [[:1-12:]] and [[:01-12:]] as options without / with leading zeros.

About the variables:

This file would look much more readable with variables that are reusing other regexes:

https://github.com/spcan/common-regex/blob/3238bc8ee85e0e000...