Re^9: Parser Performance Question (Atomic grouping)

Atomic grouping (?>...) seems to fix the problem

use strict;
use warnings;
use feature 'say';

use Data::Dump qw( pp );
my @strs =
  qw(
       "..\\"..
       "abc"
       "a\"bc"
       "a\\\\bc"
       "a\"
   );



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

  );


for my $str (@strs) {
   say "\nTesting: <$str> = ", pp ($str);
   $str =~ /$re{$_}/ and say "$_ found $&" or say "$_ found nothing"
     for keys %re;
}
[download]

Testing: <"..\"..> = "\"..\\\".."
LanX found nothing
Eily found nothing

Testing: <"abc"> = "\"abc\""
LanX found "abc"
Eily found "abc"

Testing: <"a\"bc"> = "\"a\\\"bc\""
LanX found "a\"bc"
Eily found "a\"bc"

Testing: <"a\\bc"> = "\"a\\\\bc\""
LanX found "a\\bc"
Eily found "a\\bc"

Testing: <"a\"> = "\"a\\\""
LanX found nothing
Eily found nothing
[download]

Cheers Rolf
_{(addicted to the Perl Programming Language and ☆☆☆☆ :)

Je suis Charlie!}

Comment on Re^9: Parser Performance Question (Atomic grouping) Select or Download Code

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Re^10: Parser Performance Question (Atomic grouping) by Eily (Monsignor) on Oct 06, 2017 at 12:37 UTC
I had completly forgotten about the atomic match :). I reread the documentation (because I wasn't sure what it does exactly), and it shows that it is equivalent to the possessive quantifiers. So in the spirit of TIMTOWTDI: `use strict; use warnings; use feature 'say'; use Data::Dump qw( pp ); my @strs = qw( "..\\".. "abc" "a\"bc" "a\\\\bc" "a\" ); my %re = ( LanX => qr/ " (?> \\\\ \| \\" \| [^"] )* " /x, Eily => qr/ " (?: [^"\\] \| \\. )* " /x, Poss => qr/ " (?: \\\\ \| \\" \| [^"] )*+ " /x, ); for my $str (@strs) { say "\nTesting: <$str> = ", pp ($str); $str =~ /$re{$_}/ and say "$_ found $&" or say "$_ found nothing" for keys %re; }` [download]	[reply] [d/l]
Re^11: Parser Performance Question (Atomic grouping) by LanX (Saint) on Oct 06, 2017 at 13:40 UTC
Great, discussion we (re)learned a lot! :) edit I saw atomic grouping discussed in Friedl's Book, but this use example is very instructive. And inhibiting backtracking has a great performance benefit, think I have to revisist some older projects of mine again. Cheers Rolf _{(addicted to the Perl Programming Language and ☆☆☆☆ :) Je suis Charlie!}	[reply]
Re^12: Parser Performance Question (Atomic grouping) by Eily (Monsignor) on Oct 06, 2017 at 14:03 UTC
Ah yes, I have a great potential for relearning :P	[reply]
Re^11: Parser Performance Question (Atomic grouping) by songmaster (Beadle) on Oct 20, 2017 at 01:37 UTC
I appreciate reading the conversation you guys had, sorry I wasn't to able to take part. I'm now using a slightly modified version of Eily's regex (proven using the above framework and in my own tests): `our $RXdqs = qr/ " (?> \\. \| [^"\\] )* " /x;` [download] Note that all of my `$RX...` regex variables are used inside other regexes and surrounded on both sides by `\s*` and various specific characters like parentheses and commas (this is a parser for a formally defined syntax that proceeds through the input text serially, I'm not trying to find `$needle` inside some giant `$haystack`). I do have individual tests for these variables now, previously I was only testing the parser at a higher level. - Andrew	[reply] [d/l] [select]

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