http://stackoverflow.com/questions/27109840/marpa-can-i-explicitly-disallow-keywords-as-identifiers

output

$VAR1 = \[
            'S',
            [
              'Id',
              [
                'Identifier',
                'ABC'
              ]
            ]
          ];

$VAR1 = \[
            'S',
            [
              'Id',
              [
                'Identifier',
                'ABC'
              ]
            ],
            [
              'NumLiteral',
              '42'
            ]
          ];

$VAR1 = \[
            'S',
            [
              'AND keyword',
              'AND'
            ],
            [
              'NumLiteral',
              '1'
            ]
          ];

q27109840.pl

#!/usr/bin/perl
use 5.010;
use warnings;
use strict;

use Marpa::R2;

my $grammar = 'Marpa::R2::Scanless::G'->new(
    { bless_package => 'main',
      source => \( << '__GRAMMAR__'),

:default ::= action => [ name, value]
lexeme default = action => [ name, value] latm => 1

S ::= Id
  | Id NumLiteral
  | <AND keyword> NumLiteral

Id ::= Identifier

Identifier         ~ IdentifierHeadChar IdentifierBody
IdentifierBody     ~ IdentifierBodyChar*
IdentifierHeadChar ~ [a-zA-Z_]
IdentifierBodyChar ~ [a-zA-Z0-9_]

NumLiteral ~ [0-9]+

<AND keyword> ~ 'AND'
:lexeme ~ <AND keyword> priority => 1

:discard ~ whitespace
whitespace ~ [\s]+

__GRAMMAR__
    });

use Data::Dumper;

for my $input ('ABC', 'ABC 42', 'AND 1') {
    say Dumper $grammar->parse(\$input);
}