Hi! I'm seeking some wisdom on using the Parse::RecDescent module, I'm currently making an interpreter and I want it to be able to read parentheses, here's what I have so far:

 
#!/usr/bin/perl -w

 use strict;
 use Parse::RecDescent;
 use Data::Dumper;

 use vars qw(%VARIABLE);

 # Enable warnings within the Parse::RecDescent module.

 $::RD_ERRORS = 1; # Make sure the parser dies when it encounters an e
+rror
 $::RD_WARN   = 1; # Enable warnings. This will warn on unused rules &
+c.
 $::RD_HINT   = 1; # Give out hints to help fix problems.
# $::RD_TRACE  = 1; # Trace the whole thing
 my $grammar = <<'_EOGRAMMAR_';

   # Terminals (macros that can't expand further)
   #

   startrule: instruction(s /;/) eofile

   instruction : print_instruction
               | assign_instruction

   print_instruction  : /print/i expression 
                      { print $item{expression}."\n" }
   assign_instruction : VARIABLE "=" expression
                      { $main::VARIABLE{$item{VARIABLE}} = $item{expre
+ssion} }


   expression : '(' expression ')' 
              { return $item[2] }
              | INTEGER OP expression
              { return main::expression(@item) }
              | STRING '+' expression
          { return main::concat(@item) }              
              | VARIABLE OP expression
              { return main::expression(@item) }
              | INTEGER
              | VARIABLE
              { return $main::VARIABLE{$item{VARIABLE}} }
              | STRING

   OP       : m([-+*/%])      # Mathematical operators
   INTEGER  : /[+-]?[0-9]*\.?[0-9]+/     # Signed integers
   VARIABLE : /\w[a-z0-9_]*/i # Variable
   STRING   : /'.*?'/
   eofile   : /^\Z/
 

_EOGRAMMAR_

 sub expression {
   shift;
   my ($lhs,$op,$rhs) = @_;
   $lhs = $VARIABLE{$lhs} if $lhs=~/[^-+(\.)0-9]/;
   return eval "$lhs $op $rhs";
 }
 sub concat {
  shift;
  my ($lhs,$op,$rhs) = @_;
  $lhs =~ s/^'(.*)'$/$1/;
  $rhs =~ s/^'(.*)'$/$1/;

return "$lhs$rhs"
}

 my $parser = Parse::RecDescent->new($grammar);

 #print "a=2\n";             $parser->startrule("a= 'hola '   + 3.2 ")
+;
 #print "b=1+2.2\n";           $parser->startrule("b=1+2.2");
 #print "print a\n";       $parser->startrule("print a");
 #print "print b\n";       $parser->startrule("print b");
 print "print 2+2/4\n";     $parser->startrule("print 2+2/4");
 #print "print 2+-2/4\n";    $parser->startrule("print 2+-2/4");
 #print "a = 5 ; print a\n"; $parser->startrule("a = 5 ; print a");
[download]

As you can see, I used an example on the recdescent module (which I found here http://bit.ly/Sjgdhf) and basically added strings and some other functions, as I have it now I really don't know if I have to change drastically the grammar in order to be able to read parentheses and nested parentheses.. I'd really appreciate some help on this, I've been busting my head with the trace option but have not been successful so far, any ideas??

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