Next Hook::LexWrap 4
What For?

Or design-by-contract
     wrap 'wag', 
        pre => sub { 
                 unless (UNIVERSAL::isa($_[0], 'Doggie')) {
                   die "wag()'s argument is required to be a Doggie\n";
                 }
                 unless ($_[0]->is_awake) {
                   die "violated precondition for wag():
                          Doggie argument is required to be awake\n";
                 }
               },
       post => sub {
                 unless ($_[0]->consistency_check) {
                   die "Doggie $_[0] failed consistency check
                          on return from wag()\n";
                 }
               };