comment on

Indeed, my rule of thumb isn't that good after all :-(. This snippet illustrate what you said about string vs. comment:

use strict;
my $sql = <<'--SQL--';
# this is a comment
$a = "simple string";
$b = "string and comment"; # comment

$c = "string with # thing";

# comment with "string"

$d = "very hard" # dasdas
. "to do";
--SQL--

use HOP::Lexer 'string_lexer';
my $lexer = string_lexer(
    $sql,
    [ STRING    => qr/"[^"]+"/     ],
    [ COMMENT   => qr/#[^\n]*/     ],
    [ SPACE     => qr/\s+/, sub {} ],
);

# (continues like the others...)
[download]

Here is ambiguous what to do, and both orders give a bad result. If STRING comes first, it finds strings inside comments, and if COMMENT comes first, it finds comments inside string.

(Well, there's a workaround similar to what the original article used to deal with parenthesis, which involves another parsing phase, but this is a little bit cheating I guess ;-)

use strict;
my $sql = <<'--SQL--';
# this is a comment
$a = "simple string";
$b = "string and comment"; # comment

$c = "string with # thing";   

# comment with "string"

$d = "very hard" # dasdas
. "to do";
--SQL--

use HOP::Lexer 'string_lexer';
my $lexer = string_lexer(
    $sql,
    [ STRING    => qr/"[^"]+"/     ],
    [ COMMENT   => qr/#/           ],
    [ NEWLINE   => qr/\n/          ],
    [ SPACE     => qr/\s+/, sub {} ],
);

# parse
my @out;
my $comment = 0;

while (defined (my $token = $lexer->())) {
    if (ref $token) {
        my ($label, $value) = @$token;

        $comment = 1 if $label eq 'COMMENT';
        $comment = 0 if $label eq 'NEWLINE';
        next if $label eq 'NEWLINE';
    }

    push @out, $token if not $comment;
}

# Data::Dump the output (elaborated in order to produce compact result
+s)
use Data::Dumper;
$Data::Dumper::Indent = 0;
$Data::Dumper::Terse = 1;
($\, $,) = ("\n", ",\n");
print map { Dumper $_ } @out;
[download]

Which gives us:

'$a',
'=',
['STRING','"simple string"'],
';',
'$b',
'=',
['STRING','"string and comment"'],
';',
'$c',
'=',
['STRING','"string with # thing"'],
';',
'$d',
'=',
['STRING','"very hard"'],
'.',
['STRING','"to do"'],
';'
[download]

In reply to Re^3: HOP::Lexer not doing what I expected by cmarcelo
in thread HOP::Lexer not doing what I expected by bart

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