capturing part of a recursive Parse::RecDescent production

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

Hi Folks,

I have a recursive production and I want to return an array of the all the tokens matched by 'primitive'.

(The complete grammar is rather large so I'm posting just a snippet.)

vvalue:
    primitive vector_sep(?) vvalue
    | primitive vector_sep(?)
[download]

In an attempt to see the data structure being produced, I tried this:

vvalue:
    primitive vector_sep(?) vvalue
        { \@item }
    | primitive vector_sep(?)
        { \@item }
[download]

Which according to Data:Dumper, produces the structure below from "2,3 5 7,11,13 17".

                       [
                         'vvalue',
                         '2',
                         [
                           ','
                         ],
                         [
                           'vvalue',
                           '3',
                           [],
                           [
                             'vvalue',
                             '5',
                             [],
                             [
                               'vvalue',
                               '7',
                               [
                                 ','
                               ],
                               [
                                 'vvalue',
                                 '11',
                                 [
                                   ','
                                 ],
                                 [
                                   'vvalue',
                                   '13',
                                   [],
                                   [
                                     'vvalue',
                                     '17',
                                     [],
                                     $VAR1->[6]{'value'}[3][3][3][3][3
+][3]
                                   ],
                                   $VAR1->[6]{'value'}[3][3][3][3][3]
                                 ],
                                 $VAR1->[6]{'value'}[3][3][3][3]
                               ],
                               $VAR1->[6]{'value'}[3][3][3]
                             ],
                             $VAR1->[6]{'value'}[3][3]
                           ],
                           $VAR1->[6]{'value'}[3]
                         ],
                         $VAR1->[6]{'value'}
                       ],
[download]

What I'd like to receive back is [2,3,5,7,11,13,17].

Can someone point me in the right direction?

Cheers,

-J

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Re: capturing part of a recursive Parse::RecDescent production by ikegami (Patriarch) on Feb 24, 2005 at 03:04 UTC
For starters, don't use `\@item`, use `[ @item ]`. That'll get rid of the weird junk at the end. Then you can flatten the vvalue return as follows: `vvalue : primitive vector_sep(?) vvalue { [ $item[1], @{$item[3]} ] } \| primitive vector_sep(?) { [ $item[1] ] }` [download] Your grammar can be optimized to remove unneeded backtracking. Here's a (completely) equivalent grammar: `vvalue : vvalue_(s) { [ map { @$_ } @{$item[1]} ] } vvalue_ : primitive vector_sep(?) { [ $item[1] ] }` [download] Both return: `$result = [ '2', '3', '5', '7', '11', '13', '17' ];` [download]	[reply] [d/l] [select]

Replies are listed 'Best First'.

Re: capturing part of a recursive Parse::RecDescent production
by ikegami (Patriarch) on Feb 24, 2005 at 03:04 UTC

For starters, don't use \@item, use [ @item ]. That'll get rid of the weird junk at the end. Then you can flatten the vvalue return as follows:

vvalue : primitive vector_sep(?) vvalue
         { [ $item[1], @{$item[3]} ] }
       | primitive vector_sep(?)
         { [ $item[1] ] }
[download]

Your grammar can be optimized to remove unneeded backtracking. Here's a (completely) equivalent grammar:

vvalue  : vvalue_(s)
          { [ map { @$_ } @{$item[1]} ] }
vvalue_ : primitive vector_sep(?)
          { [ $item[1] ] }
[download]

Both return:

$result = [
            '2',
            '3',
            '5',
            '7',
            '11',
            '13',
            '17'
          ];
[download]

[reply]
[d/l]
[select]