$VAR1 = [
          '4',
          '+',
          [
            '1',
            '*',
            '2'
          ]
        ];

##</code><code>##

$VAR1 = [
          [
            [
              [
                '4'
              ]
            ],
            '+',
            [
              [
                '1'
              ],
              '*',
              [
                '2'
              ]
            ]
          ]
        ];

##</code><code>##

  startrule: comparison_expr

  comparison_expr: additive_expr
               (comparison_op additive_expr { [ @item[1..2] ] })(s?)
               { [  $item[1], map { @ $_ } @{$item[2]} ] }
  comparison_op: />=?|<=?|!=|==?|le|ge|eq|ne|lt|gt/

  additive_expr: multiplicative_expr
               (additive_op multiplicative_expr { [ @item[1..2] ] })(s?)
               { [  $item[1], map { @ $_ } @{$item[2]} ] }
  additive_op: /[+-]/

  multiplicative_expr: modulus_expr
               (multiplicative_op modulus_expr { [ @item[1..2] ] })(s?)
               { [  $item[1], map { @ $_ } @{$item[2]} ] }
  multiplicative_op: /[*\/]/

  modulus_expr: paren_expr
               ('%' paren_expr { [ @item[1..2] ] })(s?)
               { [  $item[1], map { @ $_ } @{$item[2]} ] }


  paren_expr: '(' comparison_expr ')' { $item[2] }
            | number

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