use strict;
use warnings;

use Parse::RecDescent;

use vars qw(
   %item @item $return
   @pair @store
);

my $data   = do {local $/;<DATA>};
my $parser = Parse::RecDescent->new($data);

my @code = (
   q/concat(int2string(counter, 1),result)/,
   q/concat("hello","world")/,
   q/concat(foo,bar)/,
);

$parser->startrule($_) for @code;

for (0..$#code) {
   print "$code[$_]\n";
   print "\targ 1 => ", $store[$_][0], "\n";
   print "\targ 2 => ", $store[$_][1], "\n";
}

__DATA__
startrule: function

function: label open_p arg comma arg close_p

arg: nested_function | quoted_literal | literal

nested_function: label open_p arg comma arg close_p
{ 
   push @main::pair, join('', @item[1..$#item]);
   pop @main::store;
   if (@main::pair == 2) {
      push @main::store,[@main::pair];
      @main::pair = ();
   }

   $return = join('', @item[1..$#item]);
   print STDERR "nested function: $return\n";
}

quoted_literal: quote /[^"]+/ quote
{
   push @main::pair, $item[2];
   if (@main::pair == 2) {
      push @main::store,[@main::pair];
      @main::pair = ();
   }

   print STDERR "quoted literal: $item[2]\n";
   $return = $item[2];
}

literal: /\w+/i
{
   push @main::pair, $item[1];
   if (@main::pair == 2) {
      push @main::store,[@main::pair];
      @main::pair = ();
   }

   print STDERR "literal: $item[1]\n";
   $return = $item[1];
}

label: /[a-zA-Z]\w*/

open_p: /\(/

close_p: /\)/

comma: /,/

quote: /"/
[download]

jeffa

L-LL-L--L-LL-L--L-LL-L--
-R--R-RR-R--R-RR-R--R-RR
B--B--B--B--B--B--B--B--
H---H---H---H---H---H---
(the triplet paradiddle with high-hat)