my %package = qw(
  W  pack_W
  X  pack_X
  Y  pack_Y
  Z  pack_Z
);

unless (exists $package{$state}) {
  # Handle this error somehow...
  die "State '$state' is not implemented";
}

my $package_file = "$package{$state}.pm";
$package_file =~ s~::~/~g;
require($package_file);
my $app = $package{$state}->new(%stuff);
$app->run;