Question #1 is ... what do you want? (No, seriously.) What interpretation of these three strings do you want to be “correct?” Are they three distinct cases, or examples of the same one?

Sorry, I know the frustration. I see now that what I said has multiple interpretations, and that I didn't even follow what I tell others to do when posting questions like this. To clarify: I want to be able to apply my grammar to take this string:

     { hello }

...and find a match.. Then I want to be able to apply the same grammar to this string:

     {{ hello }}

...and also find a match. Then I want to be able to apply the same grammar to this string:

     {{{ hello }}}

and also find a match. By "match", I mean that my program should produce no errors, and these lines:

my $parser = Parse::RecDescent->new($grammar) 
    or die "Bad grammar!\n";

defined $parser->startrule($text) 
    or die "Can't match text";
[download]

...should not produce any output. So when I run my program three times on each of those strings, each time there should be no output at all. What I am trying to code is a backreference.

But now that I think about it, applying my desired grammar to this three line block of text:

    { hello }
    {{ hello }}
    {{{ hello }}}

...would only require a trivial adjustment to the grammar:

    startrule:  brace_block(s)    #adjustment

    brace_block:  lbrace(1..) 'hello'  <something>

    lbrace:  / [{] /xms
    rbrace: / [}] /xms
[download]

In any case, I figured out a solution. The grammar below allows me to parse 'hello', preceded by a variable number of braces, followed by the same number of braces that preceded 'hello':

    startrule: <rulevar: $rbraces>

    startrule:  lbrace(s) 
                { 
                    my $lbraces = join '', @{$item[1]};  
                    $rbraces = "}" x length $lbraces;
                }
               'hello'
               "$rbraces"
               

    lbrace: / [{] /xms
[download]

Instead of using a rule for the right braces, I am using a literal. Is there a better way to produce a backreference?

Please provide a full representative example of the type of data you need to parse, and we’ll help you write the proper grammar-mojo. It does take practice.

Yes, this is part of a larger grammar I'm working on, but I don't think posting the whole thing would be helpful. I would love to have you take a look at the complete grammar when I'm done. My current problem: when I incorporate the solution above into one of my rules, I can't get the blasted rule to return the entire match to other rules without causing the error:

Can't use string ("{{") as an ARRAY ref while "strict refs" in use at 
+(eval 14) line 377
[download]

I find it frustrating that Damian didn't use Carp, so that I could pin down exactly which line in my code is causing that error--I could care less which line in his code is causing the error. Another thing I find frustrating is that a rule doesn't return its whole match to another rule. Why in the heck is the default to return only what matched the last term of a rule? I have no idea how the default behavior would ever be useful.

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