Re^2: Random Tips on Parse::RecDescent

[Anonymous Monk]

The example in random tip #16 does not explicitly spell out that you need to :

use Text::DelimMatch;

and in the grammar definition you need a rule :

newline: "\n"

With those two things in place the code works fine for parsing multi line HTML comments.

Parsing multi line C style comments is complicated by the fact that * is a regexp character so it needs escaping. I managed to get the following code to work OK based on technique outlined in the tip. I'm sure it could be done better but I was struggling with the escaping

# Function to cope with multiline comments
# Must be placed in main section of program
sub parse_multilinecomment
{
        my $text       = shift;

        my $mc = new Text::DelimMatch( '\\/\\*', '\\*\\/' );
        my ( $p, $m, $r ) = $mc->match( '/*' . $text );

        if ($p) {
            $text = $p;
        }
        else {
            $text = "";
        }
        $text .= $r if ($r);
        $m =~ s/^\/\*//;
        $m =~ s/\*\/$//;
        return $text, $m;
 }

and the grammar rules :

    newline: "\n"
        
    multilinecomment:
        <skip: qr/[ \t]*/> newline(0..) '/*'
        {
            ($text,$return) = main::parse_multilinecomment($text);
            print $return . "\n";
             $return = ['xcomment',$return];
        }

Successfully matches the following example :

/*
    A multiple line
    /*
        with nested
    */

    comment
    
    

*/

Hope this may help someone

Adrian