Re: More re odditie [Was: regular expressions that match nothing]

[Mattias Engdegård]

16 maj 2019 kl. 20.35 skrev Michael Heerdegen <address@hidden>:
> 
> BTW, while we are here: I'm also curious whether we want to add
> nl, newline -> "\n" to rx.  I mean we have nonl and space - only for
> newlines one needs to use string syntax in rx.

Maybe, but there is no special name for any other literal string. `space' 
doesn't mean the space character but [[:space:]], or \s-, whose exact meaning 
depends on the current syntax table. (Which is sometimes very surprising; look 
at rfc2047-syntax-table!) `nonl' has plenty of legacy -- the name is from SRE, 
and even in string regexps it has a special convenience symbol.

I would much rather see a clean, robust and expressive extension mechanism for 
rx (`rx-constituents' does not count). There are various hacks and libraries 
but it probably needs to be integrated.