my $grammar = q{
  {our @a, @as}

  ruleX: r1 local_a r2 r3 unlocal_a
  local_a: {
    push(@as, \@a);
    *a{ARRAY} = undef;
  }
  unlocal_a: {
    *a{ARRAY} = pop(@as);
  }
  r2: 'keyword' /[a-z]+/ {
    local *a = \@::{$item[2]};
  }
  r3: 'value' /[a-z]+/ {
    print @a;
  }
}