p5 to p6 arg parsing try 2

# Constants
my $script = basename($0);
my $version = '0.1';

# Handle arguments
my $dbfile = "$ENV{HOME}/.config/banshee-1/banshee.db";
my $export_dir;
my $library_root;
my $msg = q[Dump all of banshee's playlists  (Banshee Playlist Export)];
@ARGV or pod2usage(-message => $msg, -exitval => 0, -verbose => 0 );
GetOptions('help'             => sub { &pod2usage(-message => $msg,
						  -exitval => 0 ) },
	   'h'                => sub { &pod2usage(-message => $msg,
						  -exitval => 0,
						  -verbose => 0 ) },
	   'man'              => sub { &pod2usage(-exitval => 0,
						  -verbose => 2 ) },
	   'version|V'        => sub { print "$script $version\n"; exit(0) },
	   'dbfile=s'         => \$dbfile,
	   'export-dir|e=s'   => \$export_dir,
	   'library-root|l=s' => \$library_root
    ) or die("Try `$script --help' for more information.\n");
die("$script: missing required argument --export-dir\n")
    unless defined $export_dir;
die("$script: export directory does not exist.\n")
    unless -e  $export_dir;
die("$script: banshee database does not exist or is not readable\n")
    unless (-f $dbfile && -r $dbfile);
$library_root = $export_dir
    unless defined $library_root;


========================================


# Constants
constant script  = $?FILE.IO.basename;
constant version = '0.1';

# Not implemented yet
#sub USAGE{
#    q[Dump all of banshee's playlists  (Banshee Playlist Export)].say;
#    $?USAGE.say;
#}

multi MAIN( Bool:D :h(:$help)   ) is hidden-from-USAGE {
    say "Print help here.";
    exit(0)
 }
multi MAIN( Bool:D :V(:$version)) is hidden-from-USAGE {
    say "{script} {version}";
    exit(0) 
}
multi MAIN( Str :e(:$export_dir)! where
                  { .IO.d // die "{script}: export directory does not exist." },
            Str :l(:$library_root) where
                  { .IO.d // die "{script}: export directory does not exist." }
                  = $export_dir,
            Str :$dbfile where
                  { .IO.f && .IO.r // die "{script}: banshee database does not "
                                          ~ " exist or is not readable" }
                  = "%*ENV<HOME>/.config/banshee-1/banshee.db"
        )
{
 
    exit 1;
}