in reply to Re^2: Parsing and translating Perl Regexes
in thread Parsing and translating Perl Regexes

And indeed your code doesn't work!
Yeah, I caught that a little late. As penance I tried to track down a hook, but couldn't find one. And so I offer up a solution using a guard. It's more intimidating, but at least it auto-expires and allows fine-grained localization. 
use strict;
use warnings;

my $log = parse_regex( q#(\\.|["']|x)# );
print $log;
warn "And STDERR is back\n";

sub parse_regex {
  my ($regex) = @_;

  # Catch and stash warnings 
  my $guard = stderr_eater(my $parselog);

  # --- compile regex
  eval q{
   use re 'debug';
   qr/$regex/;
  };

  return $parselog;
}

sub stderr_eater {
  package STDERR::Eater;

  open my $guard, '>&', STDERR;
  close STDERR;
  open STDERR, ">", \$_[0];

  return bless \$guard;
  
  sub DESTROY {
    close STDERR;
    open STDERR, ">&", $_[0];
  }
}

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My first thought was YAPE::Regex. Actually my first thought was roll my own, but that's more of a reflection on my own poor choices. It looks like there's some reasonable robustness there, but was unsure if this fell into the "online analyzers which are easily fooled". It'll at least take care of the tokenizing for you.

#11929 First ask yourself `How would I do this without a computer?' Then have the computer do it the same way.

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Re^4: Parsing and translating Perl Regexes
by LanX (Saint) on Nov 05, 2013 at 12:21 UTC
    Thanks! =)

    > I offer up a solution using a guard.

    I think you are a little too concerned about the redirection thing. I know it looks weird (at least it did the first time for me) but it's well documented in the perldocs.

    Direct hooks into the regex-engine OTOH would be nice...

    > "online analyzers which are easily fooled".

    many online solutions think PCRE means PCRE...

    > It'll at least take care of the tokenizing for you.

    actually there more levels of tracing-info which use re qw/Debug .../ may supply. (I still have to dig into perlreguts to understand it completely)

    I like the fact that Perl does the hard thing for me ... and I have this nagging feeling that only Perl can parse Perl... ;-)

    One may trust into specifications, but regarding Perl I think direct control is better. ¹

    At second thought translating to other engines is a very ambitious task, I think I should start with a simple beautifier which translates "line-noise" to a '/x'-option multiline expression.

    Ok YAPE::Regex::Explain could possibly be patched for this.

    Cheers Rolf

    ( addicted to the Perl Programming Language)

    ¹) kind of quoting a big administrator ;-)

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