I understand that the  [^\1] regex expression presented here is intended as pseudocode, but in addition to the radical changes to backrferencing it implies, there's another problem: the syntax of character classes would have to change radically to support it. Something like  \1 in a character class is compiled as an octal character representation:

c:\@Work\Perl\monks>perl -wMstrict -le
"my $rx = qr{ [\1] }xms;
 print $rx;
 print 'match' if qq{\cA} =~ $rx;
"
(?msx-i: [\1] )
match
[download]

Yes. Like LanX, you're getting bogged down in implementation.

What do you want it to do with that syntax? How would you redefine Perl regexes to do this?

I think another symbol for backref would help. (I don't know what we'd use, but that's a different problem.) Then use the same thing for forward references. And for fun, we'll call those ferkcabs.

-QM
--
Quantum Mechanics: The dreams stuff is made of

How would you redefine Perl regexes to do this?

But the  (?:[^\1]*) construct was envisioned to get around the lack of variable-width positive/negative lookbehind; I think I'd just implement that. (Of course, I suspect the reason it hasn't been implemented yet is because it's a royal pain to do so. Perhaps best to be careful what you wish for lest you find yourself with a new and very difficult assignment. As for implementing ferkcabs, I think I'd switch to another profession first. :)

---

Give a man a fish:  <%-{-{-{-<

This is because $1 is a global var will keep match instead of erasing when backtracking.

FWIW I tried something similar by capturing the following character in $2 for the next run:

m/ ^ (?:(?!\2).)*? (.) (?=(.|$)) (?!.*\1) /x

But couldn't get it to work, probably because the regex engine is not considering another defined \2 while backtracking. (or probably b/c I was too tired last night)

  DB<310> @inp = glob '{a,b}'x3


  DB<311> ;m/ ^ (?:(?!\2).)*?  (?{say "<$_ $2>"})  (.) (?=(.|$)) (?!.*
+\1) /x and say ("found $1 in $_") for @inp
<aaa >
<aab >
<aba >
<aba b>
found b in aba
<abb >
found a in abb
<baa >
found b in baa
<bab >
<bab a>
found a in bab
<bba >
<bbb >


  DB<312>
[download]

probably I'm having a bug in my logic, experts to the rescue! ;-)

Didn't have the time yet for proper debugging.

I didn't expect my forward ref to work, if that's what you thought. The regex engine would have to include a flag to indicate when the first capturing parens were seen, and do the right thing.

-QM
--
Quantum Mechanics: The dreams stuff is made of

What is the right thing???

I can only judge the implementation, which considers $1 ff to be global.

update

This demonstrates whats happening, $2 is always the next character or empty.

  DB<322> ;m/ ^ .*? (?{say "<$_ $2>"})  (.) (?=(.|$)) (*FAIL)/x
<babab >
<babab a>
<babab b>
<babab a>
<babab b>
<babab >
[download]

Cheers Rolf
_{(addicted to the Perl Programming Language and ☆☆☆☆ :)
Je suis Charlie!}