sub assert{
   my ($stmt,@args)=@_;
   my $ok=eval"$stmt" or die "Failed to eval assertion '$stmt':$@";
   unless ($ok) {
      no warnings;
      my $str=eval qq("$stmt") 
         or die "Failed to eval assertion '$stmt' as a string:$@";
      die "Failed assertion '$str'\n";
   }
}