use Parse::RecDescent qw( );
...
open(local *Parse::RecDescent::ERROR, '>', \my $error);
my $p = Parse::RecDescent->new($grammar) or die "Invalid grammar";
my $output = $p->startrule($str) or die $ParseError;

##</code><code>##

print("d");
BEGIN {
   print("b");
   BEGIN {
      print("a");
   }            # inner BEGIN     executed after this line is compiled
   print("c");
}               # outer BEGIN     executed after this line is compiled
print("e");
                # outermost scope executed after this line is compiled