in reply to Re^2: Parser Performance Question
in thread Parser Performance Question

> Please, stop talking in riddles.

Riddles are an efficient instrument for motivation in didactics. =)

For instance a friend of mine spends loads of time in hacker competitions... ;-)

> Do you mean "a\\"b"?

What do you think? xD

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

update

  DB<103> '"a\\"b"' =~  / " (?: [^"] | \\" )* " /x ; print $&        #
+ nonsense
"a\"

  DB<104> '"a\\"b"' =~  / " (?: \\" | [^"] )* " /x ; print $&        #
+ better
"a\"b"

  DB<105> '"a\\"b"' =~  / " (?: \\\\ | \\" | [^"] )* " /x ; print $& #
+ best
"a\"b"

[download]

Why #nonsense? Because the or-branch will never match, no matter which input.

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Re^4: Parser Performance Question (updated)
by Eily (Monsignor) on Oct 06, 2017 at 01:44 UTC

    The last two are still incorrect, as q< \\" > will be parsed as an escaped quote. /" (?: [^"\\] | \\. )* "/sx is the bestest solution :-P

    Edit: except when I'm an idiot and confuse (?= for (?:

[reply]
[d/l]
      > q< \\" > will be parsed as an escaped quote

      I don't understand, it IS an escaped quote and it works for me:

        DB<175> $re = qr/ " (?: \\\\ | \\" | [^"] )* " /x;

  DB<176> p $a= q<x  "..\\".."  x>
x  "..\".."  x

  DB<177> $a =~ /$re/; print $&
"..\".."

      [download]

      update

      maybe you should show us how you'd escape a double-quote.

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

[reply]
[d/l]
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        Meh, this will teach me about posting when I can't test. I meant q< \\\\" >; but thought the \ wouldn't escape the next one. The case where the \ just before the " is litteral because escaped, so it can't escape the ".

        use v5.20;
use Data::Dump qw( pp );
my $str = <<STR;
 " .. \\\\" .. "
STR

print $str;

my %re = (LanX => qr/ " (?: \\\\ | \\" | [^"] )* " /x,
          Eily => qr/ " (?: [^\\] | \\. )* " /x);

$str =~ /$re{$_}/ and say "$_ found $&" for keys %re;

        [download]
         " .. \\" .. "
Eily found " .. \\" .. "
LanX found " .. \\"

        [download]

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