PRD parser problem: How to skip C comments when parsing

Hanken has asked for the wisdom of the Perl Monks concerning the following question:

Hi, Guys, I am new to PRD. I knew there are many topics on skipping C comments in parser, but I failed to make it work in my perl script. Can anybody show me an example or just fix my script blow.

#! /usr/local/bin/perl -sw

BEGIN {
        close STDERR and open STDERR, '>./STDERR' or die $!;
}
use Parse::RecDescent;

#============================================
# GRAMMAR DEFINITION HERE
#============================================
$grammar =
q{
    Para:       List(s) /\Z/
                | { use Data::Dumper 'Dumper';
                    print "$_->[0]\n" for @{$thisparser->{errors}};
                    exit;
                    }
    List:       #<skip: here???>
                Order Name Score Prize
                | <error: error 0!>
    
    Order:       /\d+/ {print "@item\n";}
                | <error: error 1!>
                
    Name:       /\w+/ {print "@item\n";}
                | <error: Expecting a name!>
                
    Score:       /\d+/ {print "@item\n";}
                | <error: error 2!>
                
    Prize:      <skip: /\/\/.*\n/>
                /[^\n]+/ {print "@item\n";}
                      
};

#============================================
# MAIN PROGRAM STARTS HERE
#============================================

$parse = new Parse::RecDescent ($grammar);

my $text = do { local $/; <DATA> };
$parse->Para($text);


__DATA__
1   Pig  100 red flower     // 1 can this be removed? 
2   Han  80  bread          /* 2 I want this removed! */
3   Hen  50  ass kicked     /* 3 this comment should be 
                                handled too */
3   Fdi  99  rose           /* 4 failed msg if unbalanced comment here
[download]

BTW: my script works well if there is no comment in <data>.

Comment on PRD parser problem: How to skip C comments when parsing Download Code

Replies are listed 'Best First'.
Re: PRD parser problem: How to skip C comments when parsing by andreas1234567 (Vicar) on Jun 10, 2008 at 06:49 UTC
How do I use a regular expression to strip C style comments from a file? -- No matter how great and destructive your problems may seem now, remember, you've probably only seen the tip of them. [1]	[reply]
Re: PRD parser problem: How to skip C comments when parsing by ikegami (Patriarch) on Jun 10, 2008 at 07:03 UTC
Assuming you don't allow comment nesting or `//`, a C comment is `qr{ /\ .? \/ }sx` [download] You said C, but your example also shows a C++ comment. A C++ comment is `qr{ // [^\n]* }x` [download] The default definition of whitespace in PRD is `qr{ \s* }x` [download] So if we combine them all, we get `Para: <skip:qr{ (?> \s \| /\* .? \/ \| // [^\n]* )* }sx> List(s) /\Z/` [download] `<skip>` is dynamically scoped, so `List` and everything called by it will be affected.	[reply] [d/l] [select]
Re^2: PRD parser problem: How to skip C comments when parsing by Hanken (Acolyte) on Jun 10, 2008 at 07:46 UTC
Thanks ikegami! But your change seems not fix my script. I cannot get the right result when I change my script with your kind suggestion. `the error log: error 1! error 0!` [download]	[reply] [d/l]
Re^3: PRD parser problem: How to skip C comments when parsing by ikegami (Patriarch) on Jun 10, 2008 at 08:01 UTC
Did you forget to remove `<skip: /\/\/.\n/>` from `Prize`? You'll still get an error, though, because your data is invalid based on your definition of `Prize`. You've previously indicated or implied that the `Prize` is the rest of the line. You have changed you definition of `Prize` without adjusting your grammar to compensate. You probably want something like: `Prize: /(?:(?!\n\|\/\\|\/\/).)*/` [download]	[reply] [d/l] [select]
Re^4: PRD parser problem: How to skip C comments when parsing by Hanken (Acolyte) on Jun 10, 2008 at 08:40 UTC
Re^5: PRD parser problem: How to skip C comments when parsing by ikegami (Patriarch) on Jun 10, 2008 at 09:49 UTC