Re^2: Regex: matching character which happens exactly once

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
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Re^3: Regex: matching character which happens exactly once by QM (Parson) on Oct 24, 2017 at 09:16 UTC
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	[reply]
Re^4: Regex: matching character which happens exactly once by AnomalousMonk (Archbishop) on Oct 24, 2017 at 16:51 UTC
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: `<%-{-{-{-<`	[reply] [d/l] [select]