#!/usr/bin/perl -wTR
use strict;
use CGI;
use DBI;

restrict DBPassword, DB;

my DBPassword $passwd = "abcdef";
my DB $dbh = DBI->connect("DBI:mysql:something", 
                          "someone", $passwd);    # ALLOWED

my $cgi = new CGI;
print $cgi->header();

print $passwd;           # NOT ALLOWED, program terminates
print STDERR $passwd;    # NOT ALLOWED, program terminates

open(FILE, "> somefile") or die "Failed to open: $!";
print FILE $passwd;      # NOT ALLOWED, program terminates

restrict CreditCard, CreditCardGateway;

my CreditCard $credit_card = $cgi->param("credit_card");
my CreditCard $expiry = $cgi->param("expiry");

my $foo = "$credit_card $expiry";   # Foo is now 
                                     # CreditCard type too.

print $foo;         # NOT ALLOWED, program terminates
print STDERR $foo;  # NOT ALLOWED, program terminates
print FILE $foo;    # NOT ALLOWED, program terminates

my CreditCardGateway $gateway;
open ($gateway, "| cc_card_gateway") or die "failed to open gateway: $
+!";

print $gateway $foo;          # ALLOWED
print $gateway $credit_card;  # ALLOWED
print $gateway $expiry;       # ALLOWED

$foo++;       # Still of CreditCard type...
[download]

restrict CreditCard, CreditCardGateway;
filter CreditCard, \&clean_credit_card;

my CreditCard $credit_card = $cgi->param("credit_card");
print $credit_card;        # ALLOWED (filters card)

my CreditCardGateway $gateway;
open ($gateway, "| cc_card_gateway") or die "failed to open gateway: $
+!";

print $gateway $credit_card;  # ALLOWED (prints full 
                               # details)

# very very naive cleaning function
sub clean_credit_card {
    my ($restricted) = @_;

    $restricted = s/.{12}/./;  # replace 12 digits with .s 
    return $restricted;
}
[download]

So, does anyone other than pjf and I think this would be worth while?

Update: changed the title