# build_parser.pl

use strict;
use warnings;

use Parse::RecDescent qw( );

my $grammar = <<'__END_OF_GRAMMAR__';
    {
        # Lexical pragmas and lexcial variables
        # here are in the same scope as the sub
        # created for each grammar rule.

        use strict;
        use warnings;

        my %KNOWN_COMMANDS = map { $_ => 1 } qw(
           hap hccmrg hup hspp hpp hpg hdp hdlp hcp
        );
    }

    parse   : cmdline /\Z/ { $item[1] }

    cmdline : pkgcmd opt(s?) { [ @item[1,2] ] }

    pkgcmd  : IDENT pkgcmd_[ $item[1] ] { $item[1] }
    pkgcmd_ : { $KNOWN_COMMANDS{$arg[0]} }
            | <error:Unknown command>

    opt     : FLAG opt_ { [ @item[1,2] ] }
    opt_    : IDENT
            | { 1 }

    FLAG    : /-\w+/
    IDENT   : /\w+/

__END_OF_GRAMMAR__

Parse::RecDescent->Precompile($grammar, 'Parser')
   or die("Bad Grammar\n");