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

my $grammar = q`

  startrule: expression /^\Z/ { $item[1]; }
    # you can also put comments into the grammar
    # such as to explain that /^\Z/ means 'match the end of the string'
  expression:
    operand operator expression  { [@item[1..3]] } | 
    operand { $item[1] }

  number: /\d+/ { $item[1] }

  paren_expression: '(' expression ')' { $item[2] }

  operand: paren_expression { $item[1] }| 
	   number { $item[1] } 

  operator: '%' { [@item] } |
            /[*\/]/ { [@item] } |
            /[+-]/ { [@item] } |
            '=' { [@item] }

`;

my $parser = new Parse::RecDescent( $grammar ) or die "Compile error\n";

my $st = '3%2*4';
print Dumper($parser->startrule($st));

##### Printout
$VAR1 = [
          '3',
          [
            'operator',
            '%'
          ],
          [
            '2',
            [
              'operator',
              '*'
            ],
            '4'
          ]
        ];