Parse::RecDescent and nesting

b10m has asked for the wisdom of the Perl Monks concerning the following question:

I'm messing with Parse::RecDescent and stumble upon a problem with nesting. Say I have this code for example:

use strict;
use Parse::RecDescent;

my $parser = Parse::RecDescent->new(q(
        start: part(s)

        part : tag      { print ">>> $item[1] <<<\n" }
             | raw

        tag  : stag raw etag { $return = "$item{stag} $item{raw} $item
+{etag}" }
        raw  : m{([^<]+)}

        stag : m{<open>}
        etag : m{<close>}
));

$parser->start(<DATA>);
__DATA__
<open> Some content <close> <open> some <open> more content <close> <c
+lose>
[download]

The result will be that the first (non nested) content is matched, but the other one (nested example) is not.

How to parse such nesting? I can see why it doesn't work, but I can't see the solution. The documentation unfortunately is not clear on this to me :(

--
b10m

All code is usually tested, but rarely trusted.

Comment on Parse::RecDescent and nesting Download Code

Replies are listed 'Best First'.
Re: Parse::RecDescent and nesting by amw1 (Friar) on Jan 14, 2005 at 15:42 UTC
This may not be exactly what you want but it is probabbly a little closer. I added the numbers after the tags to track which open/close pair I was looking at. Left 'em in. `+ use strict; use Parse::RecDescent; my $parser = Parse::RecDescent->new(q( start: part(s) { print join("\n",@{$item[1 +]}); } part : stag part(s) etag { $return = "$item{stag +} " . join(" ", @{$item[2]}) . " $item{etag}"; } \| stag data etag { $return = "$item{stag +} $item{data} $item{etag}"; } \| data data : m{([^<]+)} stag : m{<open\d>} etag : m{<close\d>} )); $parser->start(<DATA>); __DATA__ <open1> Some content <close1> <open2> some <open3> more content <close +3> <close2>` [download] gives the following output `<open1> Some content <close1> <open2> some <open3> more content <close3> <close2>` [download] The formatting of the second clause can be twekaed with the join char. I am by no means a P::RD master, but I really enjoy playing with it. Let me know if this helps.	[reply] [d/l] [select]
Re: Parse::RecDescent and nesting by hv (Prior) on Jan 14, 2005 at 13:51 UTC
I don't see anything in your grammar that would permit such nesting. I think you can allow it simply by defining tag as `stag part etag`. Hugo	[reply] [d/l]
Parse RecDescent nesting solved (95%) by tphyahoo (Vicar) on Jan 17, 2005 at 17:03 UTC
I think you want something like the following. use strict; use Parse::RecDescent; my $parser = Parse::RecDescent->new(q( start: chunk(s) chunk: tag \| raw tag : stag raw etag { print "tag: $item[1] $item[2] $item[3]\n"; #$return = "$item{stag} $item{raw} $item{etag}" $return = "$item[1] $item[2] $item[3]"; } \| stag raw tag(s) raw etag { print "tag: $item[1] $item[2] $item[3] $item[4] $item[5]\n"; #$return = "$item{stag} $item{raw} $item{etag}" $return = "$item[1] $item[2] $item[3] $item[4] $item[5]"; } #outputs: #tag: <open> tag 1 <close> #tag: <open> tag 2 <close> #tag: <open> tag 3 b <close> #tag: <open> tag 3 a ARRAY(0x1a55ad8) tag 3 c <close> #tag: <open> tag 4 b <close> #tag: <open> tag 4 d <close> #tag: <open> tag 4 c # ARRAY(0x1a8f664) tag 4 e # <close> #tag: <open> tag 4 a # ARRAY(0x1a8f670) tag 4 f # <close> raw : m{([^<]*)} stag : m{<open>} etag : m{<close>} )); #slurp mode local $/=''; $parser->start(<DATA>); __DATA__ <open> tag 1 <close> notatag 1 <open> tag 2 <close> notatag 2 <open> tag 3 a <open> tag 3 b <close> tag 3 c <close> notatag 3 <open> tag 4 a <open> tag 4 b <close> <open> tag 4 c <open> tag 4 d <close> tag 4 e <close> tag 4 f <close> notatag 4 [download] I am 95% happy with this code. If only I wasn't getting those ugly hex refs in the output. Maybe some other monk can help with that :) thomas. UPDATE: Follow up at Parse RecDescent Nesting (Followup)	[reply] [d/l]