En op 4 december 2002 sprak Damian Conway:
> Here's a postmaturely optimized solution that makes use of the
> (?>...) metasyntax to prevent expensive and useless backtracking.
>
> You should find it runs very much faster.
>
> -----cut----------cut----------cut----------cut----------cut-----
>
> use re 'eval';
>
> our $quoted = qr/ ' [^'\\]* (?> (?> \\. [^'\\]* )* ) ' # Match 'str'
> | " [^"\\]* (?> (?> \\. [^"\\]* )* ) " # Match
> 'str'
> /x;
>
> our $element = qr/ (?> (?> [^'"{},]+ ) # Match non-special
> characters
> | \\. # Match escaped
> anything
> | $quoted # Match quoted
> anything
> | (??{$nested}) # Match
> {...,...,...}
> )
> /xs;
>
> our $nested = qr/ [{] # Match {
> (?> (?: $element , )* ) # Match list of
> subelements
> $element? # Match last
> subelement
> [}] # Match }
> /x;
>
>
> $data = <DATA>;
>
> @fields = $data =~ m/\G ( $element ) ,? /gx; # Capture elements
> repeatedly
>
> use Data::Dumper 'Dumper';
> print Dumper( @fields );
>
> __DATA__
> {1}, hello one two three four five six seven eight nine
> heat-death-of-the-universe
>
> -----cut----------cut----------cut----------cut----------cut-----
>
> Note that I also added a \G to the actual m// matcher, to ensure that
> the sequence of elements matched is actually sequential (i.e. no
> convenient skipping of inconvenient non-elements in the middle).
It definitely runs a lot faster.
However, for the original test data:
__DATA__
abc, ',def' "\"ab'c,}" xyz , fred IN { 1, "x}y",3 } x, 'z'
your original program correctly prints:
$VAR1 = 'abc';
$VAR2 = ' \',def\' "\\"ab\'c,}" xyz ';
$VAR3 = ' fred IN { 1, "x}y",3 } x';
$VAR4 = ' \'z\'
';
while your postmaturely optimized one prints:
$VAR1 = 'abc';
$VAR2 = ' ';
$VAR3 = '\',def\'';
$VAR4 = ' ';
$VAR5 = '"\\"ab\'c,}"';
$VAR6 = ' xyz ';
$VAR7 = ' fred IN ';
I tried replacing just $nested or just $element with the original
unoptimized regex but that did not help.
Will the new Perl 6 pattern matching be a vast improvement for these
sort of parsing problems?
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