Re^2: Regex::Reverse tricky test cases

See my answer to dragonchild for why. I'm sorry, I thought everybody knew about sexeger, which was probably a pretty foolish assumption. Here are a couple of regexes I've run through my program:

Before: (?i-msx:a(ab)(cd)\2\1)
After: (?i-msx:(ba)(dc)\2\1a)
Before: (?-imsx:\d+[abc]def(foo|bar))
After: (?-imsx:(oof|rab)fed[abc]\d+)
[download]

Note that the 2nd is from japhy's seminal work on the subject, and differs from his reversal: alternatives should maintain their order (foo|bar becomes oof|rab, not rab|oof).

Caution: Contents may have been coded under pressure.

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Re^3: Regex::Reverse tricky test cases by dragonchild (Archbishop) on May 17, 2005 at 13:31 UTC
Ah. I understand now. How would you reverse the following: `/(?<\d+)(A)\1/` In general, if you think something isn't in Perl, try it out, because it usually is. :-) "What is the sound of Perl? Is it not the sound of a wall that people have stopped banging their heads against?"	[reply] [d/l]
Re^4: Regex::Reverse tricky test cases by Roy Johnson (Monsignor) on May 17, 2005 at 14:03 UTC
Is that supposed to be a variable-length lookbehind (it lacks an =)? Perhaps ironically, I haven't put any handling for lookahead/behind in my program. What I would need to do is to convert lookbehinds to lookaheads, and vice-versa. Other than that, the normal reversing would work. Ok, I've done that. Program says: `Before: (?-imsx:(?<=\d+)(A)\1) After: (?-imsx:(A)\1(?=\d+))` [download] Caution: Contents may have been coded under pressure.	[reply] [d/l]
Re^5: Regex::Reverse tricky test cases by dragonchild (Archbishop) on May 17, 2005 at 14:10 UTC
You're right, I should have been more careful. The regex I was trying to write (if I'd actually tested it) should have been: `(?-imsx: ((?<=\d+))(A)\1)` - I forgot that `(?<=)` is non-capturing. Your reversal fails, in large part because I didn't give you any test input. `my $string = "123A1234"; my $regex = qr/((?<=\d+))(A)\1(.*)/; my ($num, $letter, $leftover) = $string =~ $regex; ok( $num eq '123' ); ok( $letter eq 'A' ); ok( $leftover eq '4' ); ---------------------------------------------------------- my $rev_string = "4321A321"; my $rev_regex = qr/.../; # <-- what goes here?? my ($leftover, $letter, $num) = $rev_string =~ $rev_regex; ok( $num eq '123' ); ok( $letter eq 'A' ); ok( $leftover eq '4' );` [download] In general, if you think something isn't in Perl, try it out, because it usually is. :-) "What is the sound of Perl? Is it not the sound of a wall that people have stopped banging their heads against?"	[reply] [d/l] [select]
Backreferences Make Reversing Regexes Fun for the Whole Family by japhy (Canon) on May 17, 2005 at 16:31 UTC
Re^6: Regex::Reverse tricky test cases by Roy Johnson (Monsignor) on May 17, 2005 at 14:49 UTC
Re^7: Regex::Reverse tricky test cases by dragonchild (Archbishop) on May 17, 2005 at 14:58 UTC
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