#### in the library code ###
Sub::Param::make_new_param_type($param_type_name
                                \%param_definitions,
                                \&validity_function);
...
sub some_method {
   my $param = shift;
   die "die" unless $param->isValid($param_type_name);
   ...
}
sub some_other_method {
   my $param = shift;
   die "die" unless $param->isValid($param_type_name);
   ...
}
...

### in some client
...
my $p = new Sub::Param($param_type_name);
$p->foo(1);
$p->bar('Toledo');
SomeLibrary::some_method($p);
...