Regular Expression Not Fully Simplified

[dylanmorroll]

Hi there, I've just noticed that when
(a+b)(b+$)*(b+$)+a+b
is fed into the Regular Expressions Gym, it simplifies to
(a+b)b*(b+$)
However I'm pretty sure the fully simplified regular expression should be
(a+b)b*
Since if you expand the (a+b)b* onto (b+$) you get (a+b)b*b+(a+b)b* which can be simplified to (a+b)b*?

[izuzak]

Thanks for the report, @dylanmorroll! Yeah, I agree that the regex in question could be simplified more.

There's a specific simplification rule just for that case, and it seems it kicks in as expected when you try to simplify this:

b*(b+$)

but it doesn't kick in when you try to simplify this:

(a+b)b*(b+$)

And it should kick in just the same. Not sure why it's not, though. I probably won't have time to investigate in the near future, so if someone else wants to dig in and open a pull request to fix this -- I'd be happy to review and merge! 👍