First of all all of the modules got loaded at compile time, see use for why.

So instead I would use require as follows:

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;
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Note that it is important to have a check on allowed packages for security reasons. (Never trust the user!) But for a CGI application if your naming scheme is fixed it may make sense to just use a grep to see that the package is implemented, and then produce $pack by a direct manipulation. That is slightly less code, but is less flexible.